如果想表达一个数字比另一个大多少，有很多种表达方式，如果表示倍数的话可以使用times 和as...：
The man is THREE TIMES AS OLD AS his grandson.
我们可以说3 Times As Old As, 但不能写 3 Times Older Than. 同样可以写3 Years Older Than, 但是不能写3 Years As Old As.当然使用times 的时候不一定要用as 或than ： Right: The cost of a ticket is $12, SIX TIMES the cost ten years ago.
Right: The concert was attended by 300 people, TWICE the previous attendance.
而如果想表示两个数字的加或减则要用more than 或less than ： Right: I am TEN years OLDER THAN you. Wrong: I am TEN years AS OLD AS you.
More 和less 可以当作名词代词，也可以用作形容词副词等： Right: I own MORE THAN I should. (more = noun or pronoun) Right: I own MORE SHIRTS THAN I should. (more = adjective) Right: I sleep MORE THAN I should. (more = adverb)
而其他表示数比较的词如high 和low 只能做形容词： Right: My bills are LOWER than they were last year. Wrong: I spend LOWER than I did last year. Right: I spend LESS than I did last year.
1.2不定式（有意的）与分词式（不知道结果） 我们先来看两个句子：
◆ Investors sold the stock rapidly, CAUSING panic. ◆ Investors sold the stock rapidly TO CAUSE panic.
看出意思上的差别了吗?分词表示的是一种结果，但是我们不知道investors 的用意，恐慌是有意识的还是无恴造成的。而对于不定式，investors 的用意就是要造成恐慌，但是对于不定式我们不知道这个动作所造成的后果。
1.3不定式
不定式在句子中可以充当很多成分，如名词，形容词或副词： ◆ Noun: I love TO SWIM. To swim 作为love 的宾语.
◆ Adjective: The person TO MEET is here. To meet 修饰名词person . ◆ Adverb: Sue paused TO EAT lunch. To eat 修饰动词paused .
对于不定式的使用，我们也更应该关注不定式所要表达的目的：
Right: The contractors demolished the building TO KEEP it from falling down accidentally.
demolished 的发起者是contractors ,同时也是不定式to keep的发起者，它描述了demolish 的目的，这里的it 指代building。我们再看一个例子：
Wrong: The building was demolished TO AVOID falling down accidentally. 上面的例子中building 本身不可能AVOID falling down，对于上面例子可以这样修改： The building was demolished TO KEEP IT from falling down accidentally.
这里的it 指代building ，经过这样修改，building 变成了不定式的宾语。不定式虽然可騨发名词用但还是和名词有许多不同的地方，比如不能作为介词的宾语。
1.4助动词
常见的助动词有be、have和do，对于助动词，常常可以帮助我们省去句子中一些比较长的部分：
◆ Wordy: I have never seen an aardvark, but my father has seen an aardvark. ◆ Better: I have never seen an aardvark, but my father HAS. 对于这种省略肯定需要时态上的一致，如果要转换时态就不能省略： ◆ Wrong: I have never seen an aardvark, but last year my father DID. ◆ Right: I have never seen an aardvark, but last year my father saw one. 我们再看一个例子：
◆ Wrong: Our cars were designed to inspire envy, and they ARE. ◆ Right: Our cars were designed to inspire envy, and they DO.
对于第一句，they are (inspiring ) 因为时态的改变所以inspiring 不应该被省略，而第二句They DO inspire 没有什么问题。对于助动词而言，只能指代肯定的内容而不能指代否定句：
◆ Right: Some people do not eat soup, but others DO. (= do eat soup) ◆ Right: Some people do not eat soup as others DO. (= do eat soup)
在我们以前所学的过的英语中，有时会使用be to 来表示责任或义务或者是将来的一个时间，但在在GMAT中，这种表达方式容易让人产生误解，因而采用will 或should ： ◆ Wrong: We ARE TO receive an invitation.
◆ Right: We WILL receive an invitation. OR We SHOULD receive an invitation. 最后在GMAT考试中对于表示条件时应用if ，而不用should ： ◆ Awkward: SHOULD he PASS the test, he will graduate. ◆ Right: IF he PASSES the test, he will graduate
如果我们要修饰一群事物的话可以考虑群修饰：
◆ Right: This model explains all known subatomic particles, SOME OF WHICH WERE only recently discovered.
◆ Right: This model explains all known subatomic particles, SOME OF THEM only recently discovered.
◆ Right: This model explains all known subatomic particles, SOME only recently discovered.
值得注意的是这种表达中只有which 后面是跟谓语动词，我们再看一种修饰： His head held high, Owen walked out of the store.
在上面的这个句子中His head held high修饰后面的动词walked，表示Owen走出的状态，而在His head held high这个短语中，由一个名词His head 和一个名词修饰语held high构成，对于这种修饰方法我们也可以将其放在句尾或者用with的结构来修饰： ◆ Owen walked out of the store, his head held high. ◆ Owen walked out of the store with his head held high. 我们再看一个例子：
Scientists have found high levels of iridium in certain geological formations around the world, results that suggest the cataclysmic impact of a meteor millions of years ago. 在上面的例子中，results that suggest the cataclysmic impact of a meteor millions of years ago 进一步解释了found high levels，而这个修饰又由名词results及名词修饰语that suggest... years ago ,注意这时不存在就近修饰，语意上不可能修饰world。所以对于表示主句结果的我们可以用两种方式，一种是：句尾，V-ing的形式，另一种就是这种名词加名词修饰语。而在GMAT考试中我们常常会见到一种错误的选项：
Wrong: Scientists have found high levels of iridium in certain geological formations around the world, AND THIS suggests the cataclysmic impact of a meteor millions of years ago.
GMAT不喜欢用this或that因为这种代词指代对象不明确，因为一般情况下这种代词前面要加个名词。
DO SO 可以指代句子的一整个动词，包括它的宾主，修饰语：
Quinn did not eat dinner quickly, but her brother DID SO.
在这里，do so 起的作用就相当于一个代词，而有时我们也省去so : Quinn DID NOT eat dinner quickly, but her brother DID.
DO IT 则就要明确指前面的名词：
Quinn failed to do the homework, but her brother did IT. It 指向了the homework，而这句话可以省略do
Aof B that CC修饰Aof B
在of结构中of 前面的词被of 后面的词修饰，而另一个相对次要的修饰词紧跟着接着修饰： Right: He had a way OF DODGING OPPONENTS that impressed the scouts.
上面的例子中，OF DODGING OPPONENTS修饰way而that impressed修饰前面整个名词a way OF DODGING OPPONENTS，这种情况下不要误解为DODGING OPPONENTS发起的impressed这个动作。我们再看一个例句：
An ice sheet covers 80 percent OF THE SURFACE OF GREENLAND, an area roughly the size of Alaska.
an area roughly the size of Alaska修饰80 percent of the surface of而不是GREENLAND而of the surface of Greenland需要紧跟在80 percent后。 避免因修饰语太长而导致谓语太迟出现：
Awkward: A new CEO who will transform the company by decentralizing authority to various division heads while increasing their accountability through the use of public scorecards has been hired.
这句话因为who引导的修饰语而导致动词被放在句尾，而就是因为这个句子过长所以让人读起来相当费力，正确的句子可以改成：
Right: A new CEO has been hired who will transform the company by decentralizing authority to various division heads while increasing their accountability through the use of public scorecards.
the only context in which i can remember \"a NOUN to VERB\" is a context in which the NOUN is abstract in nature. for instance:
有时为了句子的简洁我们需要把主语或宾主后置，而需要用it 取代原来的位置，对于这种形式主语或形式宾语，我们不需要去寻找它的先行词，这里有几种形式需要使用it ：
1.不定式作主语：
Awkward: TO RESIST temptation is futile.
TO RESIST temptation 作为这个句子的主语，虽然这个句子语法正确但却显得头重脚轻。可以改写为：
Right: IT is futile TO RESIST temptation.
这里的it 指代不定式TO RESIST temptation.
2.that从句作主语：
THAT we scored at all gave us encouragement.
That 引导的句子作为这句话的主语，相当于一个名词部分，但是这个句子依然头重脚轻，所以可以改成：
Right: IT gave us encouragement THAT we scored at all.
There常规上来说是一个副词意思是在那地方，但有时也把它当代词使用，其所指代的通常是表示地方的名词：
◆ Wrong: At current prices, Antarctic oil may be worth drilling for, if wells can be dug THERE and environmental concerns addressed.
◆ Right: At current prices, oil in Antarctica may be worth drilling for, if wells can be dug THERE and environmental concerns addressed.
One 通常指的不确定的，非特指的单数词：
After walking by the chocolates so many times, Roger finally had to eat ONE.
上例中的chocolate 没有特定指哪一个，而如果用其他代词如it ,they 都有明确特指哪个chocolate ：
After walking by the chocolates so many times, Roger finally had to eat THEM. 在这个例子中，Roger 吃了所有的chocolate ，而如果我们特指的是单数就要用it : After walking by the chocolates so many times, Roger finally had to eat ONE. IT was delicious, but HE could eat only half of IT.
我们先来看之前的一个例子：
The bouquet of flowers WAS a giving of love.
很明显，这里的The bouquet of 和a giving of love 在结构上平行但实际上并不平行，虽然giving 在这里是作为句词使用。而作为这种动名词来说，可以被当作名词来使用，但是词性不纯。我们可以把动名词分为两类来讨论：
1.简单的动名词：Tracking
satellites accurately is important for the space agency.
上面的例子中Tracking satellites accurately 可以被something 替换，这种动名词际上是将动词放在中间，而整体作为一个名词。
2. 复合动名词：The
accurate tracking of satellites is important for the space agency.
这种形式下，动名词被完全包含在名词词组中，通常前面有冦词或形容词，或者of 的结构中，如：the running of marathons ，marathon running 。
对于这两种动句词来说，无法相互平行，而且只有复合动名词才能与名词相平行。 Wrong: The rebels demanded the withdrawal of government forces from disputed regions, significant reductions in overall troop levels, raising the rebel flag on holidays, AND a general pardon.
Withdrawal, reductions, 和 pardon 都是名词，所以这里不能使用raising ，而且这样使用容易让我误解为是一种修饰。
Right: The rebels demanded the withdrawal of government forces from disputed regions, significant reductions in overall troop levels, THE raising OF the rebel flag on holidays, AND a general pardon.
当然如果存在这种名词我们还是要选择单纯的名词而不是动名词：
◆ Wrong: The rebels demanded the withdrawal of government forces from disputed regions AND releasing certain political prisoners.
◆ Wrong: The rebels demanded the withdrawal of government forces from disputed regions AND THE releasing OF certain political prisoners.
◆ Right: The rebels demanded the withdrawal of government forces from disputed regions AND THE RELEASE OF certain political prisoners.
短的句子固然简洁但其也要注意不要为了追求简洁而造成句意混乱。在GMAT考试中，出题者会故意使用简短的句子作为错误选项来干扰正确选项。
不要为了追求简洁而删除介词短语：
◆ Too Short: I talked to the BOSTON SOLDIER. ◆ Better: I talked to the SOLDIER FROM BOSTON.
上面的例子中BOSTON SOLDIER 容易让我误解为一种特殊的士兵。所以对于这种介词短语不要轻易省略。但是对于OF 我们却可以进行转换：
A wall OF stone OR A stone wall 这里我们用到名词修饰的概念。但是对于有时间跨度，数量或有测量意思的词则不能用of 结构进行替换：
◆ Too Short: Memorial Day week OR Memorial Day’s week ◆ Better: the week OF Memorial Day ◆ Too Short: the merger year ◆ Better: the year OF the merger ◆ Too Short: the oxygen amount ◆ Better: the amount OF oxygen
◆ Too Short: the honeybee population density OR the honeybee population’s density ◆ Better: the density OF the honeybee population
下面我们列举了些在GMAT中认为太短表述不清的词： ◆ Too Short: Aegean Sea salt ◆ Better: salt FROM the Aegean Sea ◆ Too Short: Ural Mountain ore ◆ Better: ore FROM the Ural Mountains
◆ Too Short: Danube River access ◆ Better: access TO the Danube River ◆ Too Shor
所谓简洁并不意味着越短越好，同时简洁也是在比较完句意及语法错误后才使用的最后一部，但是对于简洁而言，依然有许多规则。
1. 动词优于形容词或副词，而形容词和副词又优于名词：
◆ Wordy: The townspeople’s REVOLUTION WAS AGAINST the king. ◆ Better: The townspeople REVOLTED AGAINST the king. ◆ Wordy: The artist WAS INFLUENTIAL TO the movement. ◆ Better: The artist INFLUENCED the movement.
◆ Wordy: THERE IS AN ABUNDANCE OF funds for school construction. ◆ Better: Funds for school construction ARE ABUNDANT.
因为形容词本身就是用来修饰动词，能用形容词表达的肯定好于名词。而对于动词，其也明显优于句子或短语：
◆ Wordy: They are subject to the applicability of rules. ◆ Better: Rules apply to them.
◆ Wordy: His conception of money was as a goal. ◆ Wordy: His conception of money was as a goal. ◆ Better: He conceived of money as a goal.
◆ Wordy: The cost of storms to the country is billions. ◆ Better: Storms cost the country billions. ◆ Wordy: Her decision was to go. ◆ Better: She decided to go.
◆ Wordy: His example was an influence on me. ◆ Better: His example influenced me.
◆ Wordy: Her example was an inspiration to me. ◆ Better: Her example inspired me.
◆ Wordy: They made a reference to the strike. ◆ Better: They referred to the strike.
◆ Wordy: The weight of the apples is a pound. ◆ Better: The apples weigh a pound.
2. that +v. 优于其他名词短语：
◆ Wordy: The hypothesis ABOUT the COMPOSITION OF the universe AS largely dark energy seems strange.
◆ Better: The hypothesis THAT the universe IS largely COMPOSED OF dark energy seems strange.
当我们关注一堆名词短语时不如想想that 打头引导的句子，当然这些句子中都含有动词。动词就好比一个句子的心脏，有了动词句子就能更加准确简洁的表达现其意思。
3. 形容词好于介词短语：
◆ Wordy: Oil prices have fallen, but prices at the gasoline pump have not fallen TO A COMPARABLE EXTENT.
◆ Better: Oil prices have fallen, but prices at the gasoline pump have not fallen COMPARABLY.
因为介词短语都有名词，形容词肯定优于介词短语： ◆ Wordy: to a considerable extent ◆ Better: considerably
◆ Wordy: to a significant degree ◆ Better: significantly
4. 形容词好于带有还有BE 动词的形容词子:
所以可以发现，对于冗余的结构常常用的是to be 的形式，因为用了to be 就会用到形容词名词等，而不会选择用动词或其他词：
◆ Wordy: Marcos is a professor WHO IS ADMIRABLE.
◆ Better: Marcos is an ADMIRABLE professor. 这条规则特别适用于名词修饰其他名词：
◆ Wordy: Joan, WHO IS a FIREFIGHTER, works in Yosemite Park. ◆ Better: Joan, a FIREFIGHTER, works in Yosemite Park.
5. 对于it is …that… 在不影响句意的情况下尽量不使用： ◆ Wordy: IT IS without fear THAT children should play. ◆ Better: Children should play without fear.
我们知道对于第一个句子其实是起到强调作用的，但是在GMAT考试中我们并不喜欢用这种表达方式。 总之，对于简洁而言只是最后的一个方法，不要轻易一开始就使用简洁，不要一看到the fact that, being就把选项删除，现在考试中很多正确的答案都相当冗余但句意和语法上没有太大问题。
英语的数中有可数的也有不可数的，而对于可数名词和不可数名词其所需要修饰的词不一样。 more 、most 、enough 、all 可以修饰可数名词或不可数名词。对于numbers的比较应该使用greater 而不是more than。
GMAT的SC部分常会遇到四种标点：
逗号(，)是最常见的标点，也是最难使用正确的标点，不过GMAT考试很少以标点作为考点并通过逗号来判断正确选项。关于逗号记住：
不要用逗号连接两个句子。
当句子中两个谓语动词发起者是同一个人时，不要在and 前面加上逗号。 ◆ Wrong: Earl walked to school, AND later ate his lunch. ◆ Right: Earl walked to school AND later ate his lunch. ◆ Right: Earl walked to school, AND HE later ate his lunch.
分号(;)连接两个相关的语句，每个部分都可以独自站立作为一个句子，但是如果句意上前后两者是有从属关系的则不能用分号：
◆ Right: The dam has created dead zones, WHERE fish have disappeared. ◆ Wrong: The dam has created dead zones; fish have disappeared.
分号又常常同些连接副词一起使用，如however, therefore, or in addition ，注意这些词和连词and 等又完全不相同，所以对于这些词，常常使用分号进行连接：
◆ Wrong: Andrew and Lisa are inseparable, THEREFORE, we never see themb apart.
◆ Right: Andrew and Lisa are inseparable; THEREFORE, we never see them apart.
而另一种比较少用的分号使用方法是将同一类的东西分开，而这些东西之间是用逗号分隔的：
◆ Wrong: I listen to Earth, Wind & Fire, Wow, Owls, and Blood, Sweat & Tears. ◆ Right: I listen to Earth, Wind & Fire; Wow, Owls; and Blood, Sweat & Tears.
冒号(:)为之前的事提供进一步的解释，说明。冒号前的通常是一个句子，可以独立存在，而冒号后则无需是句子，而有时会在冒号后加入namely 或that is。 I love listening to many kinds of music: namely, classical, rock, rap, and pop.
要说明的部分离冒号越近越好：
◆ Worse: Three factors affect the rate of a reaction: concentration, surface area, and temperature.
◆ Better: The rate of a reaction is affected by three factors: concentration, surface area, and temperature.
破折号( - )是一个灵活的标点符号，GMAT考试中偶尔会用到。有时破折号可以代替逗号来使用：
By January 2, 2000, the so-called “Y2K problem” was already widely considered a joke—although the reason for the non-event was the huge corporate and governmental investment in prior countermeasures.
但有时候破折号又是必须的：
My three best friends—Danny, Jimmy, and Joey—and I went skiing.
这句话如果用逗号就会让人误以为有七个人go skiing 。破折号有时用来解释或重复之前句子的某个部分，但不像冒号需要紧跟着需要解释的词前面：
Post-MBA compensation for investment bankers tends to surge far ahead of that for management consultants—by tens, if not hundreds, of thousands of dollars a year. 上面的这个例子中by tens, if not hundreds, of thousands of dollars a year 解释句子前面的far。
一个完整句子通常由短语或从句组成，而句与句之间的连接部分就要使用连词。一个句子至少含有一个主句，所谓主句就是一个句子有主语，谓语，并且能独立存在而不以because、if等引导。一个句子可以有多个主句，但主句间不能用逗号连接而应该用连词进行连接，例如：
Wrong: I need to relax, I have so many things to do! 上面的句子可以修改为：
Right: I need to relax, BUT I have so many things to do!
像and 、but 、or 、for 、yet 、nor 、so 这些都是常见的并列连词。而and 又是最常见的连词，可以用来罗列事物如：apples, grapes, AND pears 也可以用来连接句子如： I like apples, AND she likes grapes。
从属连词如：because 、although 引导从句，附属于主句。有时可以用逗号+从句来与主句进行连接，对主句进行说明：
◆ Right: I need to relax, BECAUSE I have so many things to do!
◆ Right: ALTHOUGH new data from the Labor Department indicate that producer prices rose rapidly last month, some analysts contend that the economic slowdown in the euro zone and in Asia will stem the rise in commodity prices, lessening inflationary pressures in the United States.
在连词的使用过程中，要注意不要过多的使用连词而丢失了主句： ◆ Wrong: ALTHOUGH I need to relax, YET I have so many things to do! ◆ Right: ALTHOUGH I need to relax, I have so many things to do! ◆ Right: I need to relax, YET I have so many things to do!
而在选择使用哪个名词的时候也要注意所选名词与句中的整体句意是否相符： Wrong: She is not interested in sports, AND she likes watching them on TV.
上面的前后两个句子在句意上应该是相对的两个部分，所以可以换个连词来表达： ◆ Right: She is not interested in sports, BUT she likes watching them on TV. ◆ Right: ALTHOUGH she is not interested in sports, she likes watching them on TV.
下面是一些常见的连词：
Coordinating Conjunctions: For / And / Nor /But / Or / Yet / So
Subordinators: Although / Because / Before /After / Since / When / If / Unless / That / Though / While
我们再看一个例子：
Citizens of many countries are expressing concern about the environmental damage caused by the widespread release of greenhouse gases may be impossible to reverse. 在这个例子中，前半部分Citizens of many countries are expressing concern about the environmental damage caused by the widespread release of greenhouse gases 非常正确，但是剩下的部分may be impossible to reverse 的主语是谁?句意上来说environmental damage 是其主语，但是environmental damage 不可能既是about 的宾语又是may be 的主语。所以这个句子可以这样将about 改为that ：
Citizens of many countries are expressing concern THAT the environmental damage caused by the widespread release of greenhouse gases may be impossible to reverse. 另一种改法是在may be impossible to reverse 前面加入名词，这种在GMAT考试中非常常见，特别是一些指代不清的情况下，通常出题者会用逗号加名词来解释说明后面的部分：
Citizens of many countries are expressing concern about the environmental damage caused by the widespread release of greenhouse gases, DAMAGE THAT may be impossible to reverse.
在上面的例子中我们发现，对于比较常常会将第二部分的比较词进行舍去。常见的省略形式之一是将比较的第二个所有格后的名词省略： ◆ My car is bigger than Brian’s [car]. ◆ My car is bigger than Brian’s [car]. ◆ My car is bigger than the Smiths’ [car]. ◆ My toes are longer than Brian’s [toes]. ◆ My toes are longer than the Smiths’ [toes].
对于省略我们也可以将比较第二部分中的动词，词组，甚至一整个句子省略，当然前提是不会造成歧义。
◆ Whereas I drink 2 quarts of milk a day, my friend drinks 3 [quarts]. ◆ I walk faster than Brian [walks].
◆ I walk as fast now as [I walked] when I was younger.
而有时为了避免产生歧义我们也会加入助动词，如be ,do 和have 等：
◆ Ambiguous: I like cheese more than Yvette. (Yvette could be subject or object.) ◆ Right: I like cheese more than Yvette DOES. (= than Yvette likes cheese)
◆ Right: I like cheese more than I DO Yvette. (= than I like Yvette)
而在GMAT考试中，有时也容许不需要的助动词的存在： ◆ Right: Apples are more healthy to eat than caramels.
◆ Right: Apples are more healthy to eat than caramels ARE. 所以在考试中，我们不要因为多余的助动词而排除了正确的选项。 比较必须是逻辑上平行。也就是说，必须比较同一类的事情。 ◆ Frank’s build, LIKE his brother, is broad and muscular.
上面的例句中用Frank’s build 和 his brother 进行比较，这在逻辑意义上不平行。所以正确的应该是：
◆ Frank’s build, LIKE his brother’s, is broad and muscular. 或者： ◆ Frank, LIKE his brother, has a broad and muscular build.
上面的例子中我们可以使用that 来代替build ，而如果是复数的话就要用those 来替换：
◆ Frank’s toes, LIKE THOSE of his brother, are short and hairy.
比较也需要结构上平行，也就是说相似的语法结构：
◆ I like to run through forests more than I enjoy walking through crowds.
上面的例子中run through forests 和walking through crowds 两个比较对象并不平行。To run 作为不定式，而walking 则是作为一个名词来使用，所以正确的可以写成： ◆ I like running through forests MORE THAN walking through crowds.
like 和as 是比较常见的比较词，like 是介词，也就意味着其后面需要加名词，代词或名词短语，不能加句子或介词短语。而对于as 可以当作介词或连词，也就是说其后面可以跟名词性的成分或句子：
◆ Wrong: LIKE her brother DID, Ava aced the test. ◆ Right: AS her brother DID, Ava aced the test.
上例中her brother DID 是一个句子，其为谓语动词是did，所以要用as来进行连接。 like 指相似的意思，作为介词后面必须跟名词，用来修饰前面的动词或名词，来形成一种比较。在SC部分，特别要注意在句尾的like : (1) I want to coach divers LIKE Greg Louganis.
= I want to coach divers WHO ARE LIKE Greg Louganis. OR
= I want to coach divers IN THE SAME WAY AS Greg Louganis does. (2) I want to coach divers, LIKE Greg Louganis. 注意like 前面的逗号。
= LIKE Greg Louganis, I want to coach divers. (他coaches divers而我也想这么做)
unlike 在GMAT考试中很常见，其用法和like 相同，在句尾只要不产生歧义就行： Most materials under a wide range of conditions resist the flow of electric current to some degree, UNLIKE superconductors, which demonstrate zero electrical resistance. 注：like 在平时会被人误用作表示列举，但在gmat中只有such as 才有这功能。 而as 可以作为介词也可以作为连词，当as 作为连词的时候通常的用法有这几种： ◆表示持续的As: AS I strolled to the store, I smelled the air. (= while, during) ◆表示原因的As: I will not tell you, AS you already know. (= since, because) ◆表示比较的As: You should walk AS she wants you to. (= in the same way)
而表示比较的as 在GMAT考试中是最重要的一种用法，有时会和just, so, 还有so too 连用。
◆ JUST AS the trains were late yesterday, the buses are late today. ◆ JUST AS the trains were late yesterday, SO TOO are they late today. 而作比较用的as 不单单只能边句子，也可以连接短语： AS in the previous case, the judge took an early break.
当as 作为介词使用时，也基本满足下面三种用法：
◆表示作用的As: AS your leader, I am in charge. (= in the role of) ◆表示相等的As: I think of you AS my friend. (= you are my friend) ◆表示阶段的As: AS a child, I thought I could fly. (= when I was)
而对于当介词用的as 并没有相似的意思：
◆ I will jump up LIKE a clown. (= in a clownish manner) ◆ I will jump up AS a clown. (= in a clown suit!)
所以要使用as 来比较就要在句子中使用，最常用的as 的用法是as ... as... 第一个as 后跟形容词或副词，第二个as 后跟名词、短语甚至句子。
GMAT考试中被动与主动是常出考点的地方。在被动式中的发起者常用介词by 来引导出，而如果是方式或工具则用through 或because of 。对于这种表达方式如果使用主动则会显得句子过长并且容易造成歧义：
◆ Wrong: The pizza WAS accidentally EATEN BY a quirk of fate. ◆ Wrong: A quirk of fate accidentally ate the pizza.
◆ Right: THROUGH a quirk of fate, the pizza WAS accidentally EATEN.
但是被动的句子不都是错误的句子，只是在意思相同的情况下有时会稍逊于主动表达的句子：
◆ Passive: It HAS BEEN DECIDED by Jason that he will not attend college. ◆ Active: Jason HAS DECIDED not to attend college.
但是这并不代表所有被动都不正确，只是说在句意相同的情况下主动更好。我们再看一个例子：
During this operation, new blood vessels are inserted, bypassing blockages.
上面的这句话使用了inserted 这个词，并没有产生任何歧义或者冗余，上面的话强调了blood vessels inserted而非谁发起了这个动作。对于被动态出现的标志词是by ，而在句子中并不一定非要被动和主动出现平行，当然如果能平行就更好了。
GMAT考试中常用到的另一种虚拟语气是命令语气，其意思是命令别人去执行某件事，常常由某些带命令的动词发起，如require 或 propose ： ◆ The agency REQUIRED that Gary BE ready before noon. ◆ We PROPOSE that the school board DISBAND.
上面的例子中Be 和 Disband 都是命令虚拟语气，而这种命令虚拟语气等同于直接命令对方：
◆ BE ready before noon, Gary! ◆ DISBAND, school board!
在这种虚拟语气中，不定式省略to ，(to be 改为be 而不用is，are，am)第三人称单数动词后不需要加S 。这种命令式的虚拟语气常用的结构为： 动词+that+主语+命令虚拟语气
We PROPOSE THAT the school board DISBAND.
在这种结构中that 不能省略并且绝不允许出现should。命令虚拟语气的难点在于不是所有命令动词都需要使用虚拟语气，而大多数的命令语气都不能使用虚拟语气，例如want ，而应该使用不定式：
◆ Right: The vice-president WANTS her TO GO to the retreat. ◆ Wrong: The vice-president WANTS THAT she GO to the retreat.
而对于哪些动词是需要使用不定式哪些是要使用虚拟语气，这由英语的习语决定，我们能做的只是把这些词记住。
◆只能用虚拟语气的动词：demand, dictate, insist, mandate, propose, recommend, request, stipulate, suggest
◆只能用不定式的动词：advise, allow, forbid, persuade, want
◆虚拟语气和不定式都可以使用的：ask, beg, intend, order, prefer, urge, require 而命令虚拟语气同样试用于由命令动词衍生的名词： His demand THAT he BE paid full severance was not met.
使用if 的句子一定都是虚拟语气。而if 和then 的结构有多种形式： ◆ IF you study diligently, [THEN] you will score highly. ◆ You will score highly IF you study diligently.
Then 在虚拟语气中常常被省略，同是if 也不见得都在首句中出现。下面是常见的if then 的五种结构(在这五种结构中不能在if 引导的句子中出现would ，而且一整句话都不能出现should 在if then 结构中)： 1. 不存在不确定性的情况：
◆ IF Sophie EATS pizza, THEN she BECOMES ill. ◆ IF Present, THEN Present.
这种情况比较像whenever ：WHENEVER Sophie EATS pizza, she BECOMES ill. 2. 存在一些不确定性的情况：
◆ IF Sophie EATS pizza, THEN she MAY BECOME ill. ◆ IF Present, THEN Can or May.
3. 将来时不存在不确定性
◆ IF Sophie EATS pizza tomorrow, THEN she WILL BECOME ill. ◆ If Sophie HAS EATEN pizza, then she WILL BECOME ill. ◆ IF Present, THEN Future.
4. 将来时不太可能发生
◆ IF Sophie ATE pizza tomorrow, THEN she WOULD BECOME ill. ◆ IF Hypothetical Subjunctive, THEN Conditional.
这里作者认为Sophie 不大可能吃pizza，这里用到了would，这里的would 可以用could 来替代。
5. 从不可能发生
◆ IF Sophie HAD EATEN pizza yesterday, THEN she WOULD HAVE BECOME ill. ◆ IF Past Perfect, THEN Conditional Perfect.
GMAT更喜欢简单的句子，一个能用一般时表述的句子就尽量不用完成时来表达： ◆ Joe LEARNED about an epoch in which dinosaurs HAD WALKED the earth. ◆ Joe LEARNED about an epoch in which dinosaurs WALKED the earth.
HAD WALKED 的确发生在LEARNED 之前，但是这个动作系列却没必要对其进行强调。如果一个动作发生在过去持续到现在或强调其影响时我们使用现在完成时，如果一个动词比过去的一个动词更早的发生，且强调这个时间的顺序时才用过去完成时。
如果两个动作在过去不同的时间发生，我们就用过去完成时表示更早的动作，而用过去式表示稍迟的动作。过去完成时的定义是过去的过去。
不要因为这件事是很久以前发生而没有后来的过去动作就使用过去完成时，如果只是单纯的表达过去的事同样可以使用一般过去式，比如：An asteroid STRUCK the earth millions of years ago. 从句意上来说，我们不要因为要表示过去更早的动作就选择过去完成时，我们使用过去完成时是为了强调过去的一系列事情。而且如果过去的动作发生顺序相当明显则也无需使用过去完成时，例如：Antonio DROVE to the store and BOUGHT some ice cream.
很明显DROVE 早BOUGHT 之前发生，所以由相同主语发起的先后动作，如果句意上没有强调可以不必使用过去完成时，而直接使用一般过去时即可。我们再看一个例子： Antonio DROVE to the store, and Cristina BOUGHT some ice cream.
上面的例子两个主句由and 连接，而我们并没有强调动作的顺序，所以由and 或or 连接的句子并无要求一定要使用过去完成时。同样的词还有after 和before ，因为其已经很明确的表明了动作的先后顺序，所以再用过去完成时就显得多余：
Laura LOCKED the deadbolt before she LEFT for work.
使用过去完成时时并不一定需要在句子中出现过去式，我们可以加入一个日期或一段时间，例如：
By 1945, the United States HAD BEEN at war for several years. 现在完成时表示过去的动作在过去开始并持续到现在，所以它的起点一个在过去，而终点在现在。
◆ Right: We HAVE LIVED in a hut for three days.
这个句子表明三天前我们在小屋里而现在我们依然住在小屋里。而如果句子用过去时则是另外一种意思：
◆ Right: We LIVED in a hut for three days.
这个例子意味着，我们已不再生活在小屋，而这三日已经过去了。而通常完成时里会有明显的时间状态表示这个动作发生了多久：
◆ This country HAS ENFORCED strict immigration laws for thirty years. ◆ They HAVE KNOWN each other since 1987.
上面的例子的动作都是发生在过去并持续到现在，其时间上用了for thirty years 和 since 1987,进行暗示，表达了这个动作进行了多长时间。而有时候现在完成时也表示动作已经结束，只是他的影响持续到现在：
◆ The child HAS DRAWN a square in the sand.
这个小孩不再画了，其动作已经结束但是其所画的依然存在，而如果所话内容消失了我们则要使用一般过去式。
◆ Right: The child DREW a square in the sand, but the ocean ERASED it. ◆ Right: The child DREW a square in the sand, but the ocean HAS ERASED it. ◆ Awkward: The child HAS DRAWN a square in the sand, but the ocean HAS ERASED it.
上面的例子中，erase 的时态可以是一般过去时也可以是现在完成时，第一个句子中sand 现在的状态是未知的，而第二句中sand 现在的状态是确定的，因为用现在完成时可以知道其对现在的影响。所以总结一下，现在完成时表示持续的动作或已经结束的动作的持
续影响，而since 还有within (如within the past five minutes 或者within the last ten days)，就是现在完成时重要的标志：
◆ Wrong: Since 1986 no one BROKE that world record. ◆ Right: Since 1986 no one HAS BROKEN that world record.
如果我们想谈论一个已经特定，已经结束的时期，则应当用一般过去式而非现在完成时： ◆ Wrong: Veronica HAS TRAVELED all over the world in 2007. ◆ Right: Veronica TRAVELED all over the world in 2007.
上面的第一个句子中，如果省略n 2007 则也是一个正确的句子，因为就变成了强调其对现在的影响。现在完成时在强调对现的影响时其效果要强于一般现在进和一般过去时和过去完成时。
最后，也可以将一个现在完成时放在一个ing的词前面，不定式或者从句前面表示用来表达动作结束。
◆ She WILL PAY you when you ASK her. WILL PAY 时间上是和ASK 一致的。
◆ She WILL PAY you when you HAVE TAKEN out the garbage. WILL PAY 时间上要晚于HAVE TAKEN out 多个动作的句子其动词时态应由句子的意思来决定：
◆ She WAS PLAYING with her friends when the babysitter ARRIVED. ◆ She PLAYED with her friends when the babysitter ARRIVED.
第一个句子表示当babysitter 来的时候she 正在play with her friends. 第二个句子表示当babysitter 来了以后 she play with her friends .
一般时通常用来描述事情的永久状态或常常发生的事。例如： ◆ SIMPLE PRESENT Sandy PLAYS well with her friends. ◆ SIMPLE PAST Sandy PLAYED well with her friends yesterday. ◆ SIMPLE FUTURE Sandy WILL PLAY well with her friends tomorrow.
进行时表示动作正在进行：
◆ PRESENT PROGRESSIVE Sandy IS PLAYING soccer.
◆ PAST PROGRESSIVE Sandy WAS PLAYING soccer yesterday. ◆ FUTURE PROGRESSIVE Sandy WILL BE PLAYING soccer tomorrow.
上面的例子表示说Sandy 正在PLAYING soccer ，而一般现在时：Sandy plays soccer,则是强调Sandy 比较经常或者她知道如何plays soccer 。在一般的定义中我们通常避免使用进行时而使用一般时：
◆ Wrong: Cherenkov radiation is light that particles ARE EMITTING when they ARE TRAVELING faster than the effective speed of light in any medium.
◆ Right: Cherenkov radiation is light that particles EMIT when they TRAVEL faster than the effective speed of light in any medium.
表达一般状态的动词一般不用进行时，例如know or signify： ◆ Wrong: This inscription IS SIGNIFYING the emperor’s birth. ◆ Right: This inscription SIGNIFIES the emperor’s birth. 我们先看个常见的错句：
Wrong: Crime has recently decreased in our neighborhood, WHICH has led to a rise in property values.
原句想要表达的意思是the recent decrease in crime has led to a rise in property
values ，但是使用which 意思则变为which 前面最接近的名词，而不是前面的整个句子。所以正确的可以改为：
Right: Crime has recently decreased in our neighborhood, leading to a rise in property values.
而v+ing的用法非常灵活，可以直接修饰名词(the changing seasons )，也可以修饰动词及其主语(I lifted the weight, whistling)甚至可以修饰整个句子如上例，只要这句子能能转换为名词性句子。之前的两个例子很好的说明了这个变化，我们可以表达：the recent decrease in crime... has led to a rise, 我们也可以这样表达： crime has recently
decreased... leading to a rise，这种以ing形式作表达主句的结果最为理想，不易让人产生疑问。
名词修饰常常由关系代词引导：Which That Who Whose Whom Where When
对于这些关系代词的使用有一定限制，例如：who 和whom 要修饰人，而which 则一定修饰物，而在GAMT的语法中,that 也不能修饰人，所以修饰人的词有Who, Whose or Whom ，而That 和 Which 则无法修饰人：
◆ Wrong: The scientists THAT made the discovery were rewarded. ◆ Right: The scientists WHO made the discovery were rewarded. 而Which 或whom 可以跟在介词后面:
the canal through which water flows; the senator for whom we worked.
Who 在从句中作主语，而whom 则作动词或介词的宾语： ◆ Wrong: The security guard WHO we met was nice. ◆ Right: The security guard WHOM we met was nice.
That 和 whom 从句中作宾语时可以省略：
◆ Right: The movie THAT we watched last Friday was scary. ◆ Right: The movie we watched last Friday was scary.
where可以用来修改地方名词，area, site, country or Nevada ，但是无法修饰“隐喻”地方的词如：condition, situation, case, circumstances, or arrangement，而要修饰这些词则应该用in which ：
◆ Wrong: We had an arrangement WHERE he cooked and I cleaned. ◆ Right: We had an arrangement IN WHICH he cooked and I cleaned.
When 可以指代事件或时间，如：period, age, 1987, or decade ，这里in which 也可以替换when.
我们先来看一个例子：
◆ The mansion PAINTED RED is owned by the Lees.
上例中的PAINTED RED 就是一上必要的修饰语，因为如果没有PAINTED RED就会造成很多疑问。
我们再看一个例子：
◆ This mansion, RECENTLY PAINTED RED, is owned by the Lees.
上例中，RECENTLY PAINTED RED就是非必须的修饰。因为我们知道This 已经说明清楚所要讨论的mansion。
可以用标点符号修饰必须名词和非必须名词。对于非必须修饰可以用逗号将其中间隔开，而必须修饰则不用逗号。所以一个比较常见的标志就是which 和that ，当用which+逗号，常常用来进行一上说明，即非必须修饰，而直接用that 则进行必须修饰。
我们再来看一个例子：
◆ This mansion, WHICH HAS BEEN RECENTLY PAINTED RED, is owned by the Lees.
◆ The mansion THAT HAS BEEN PAINTED RED is owned by the Lees.
动词修饰语主要修饰动词。主要是为了解释动词“how,” “when,” “where,” “why,”，通常这种词都是副词或类似副词的短语。 类型 副词 位置 举例 动词前 FREQUENTLY, I walk to the store. I FREQUENTLY walk to the store. 动词后 I walk to the store FREQUENTLY. 介词 主从连词
动词前 On Mondays, I walk to the store. 动词后 I walk to the store On Mondays. 动词前 WHEN my car is broken, I walk to the store. 动词后 I walk to the store WHEN my car is broken. 而作为从句一般打头的引导词有：because, although, if, unless, while, so that, while 有些动词修饰语可能适用于动词和动词的主语，在这些情况下，我们必须确保主语及和修饰语同样有意义。 类型 现在分词 介词+动名词 不定式表目的 位置 举例 动词前 WHISTLING “Beat It”, I lifted the weight. 动词后 I lifted the weight, WHISTLING “Beat It”. 动词前 BY CONCENTRATING, I lifted the weight. 动词后 I lift the weight BY CONCENTRATING. 动词前 TO FREE my leg, I lifted the weight. 动词后 I lifted the weight TO FREE my leg. 动词修饰语和名词修饰语不同的是动词修饰语不必紧贴着动词，距离可以比较远。但为了避免句意上的问题我们还是建议两者距离最好不要太远： ◆ Wrong: The nameless symphony was at last performed, decades after it was composed, yesterday. ◆ Right: The nameless symphony was at last performed yesterday, decades after it was composed.
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