A.语法复习
a)句法
按照语法结构及句子之间的关系可将句子划分为3类：简单句，并列句和主从句。
(1)简单句
整个句子中只有一个主谓结构，不含从句。在这一主谓结构中，可以是多个主语(合作主语)共享一个谓语，也可以是多个谓语(合作谓语)共享一个主语。如: Steve and I went to the cinema last night. I looked round but saw nobody.
(2)并列句
整个句子由两个或者更多个互不依赖，互不修饰，平行并列的主谓结构构成了并列句。并列句通常由并列连词连接。这些并列连词包括:and, but, or, nor, so, yet, for, otherw ise, li kewise, however, nevertheless, while, whereas, though, only, both...and, not on ly...but also, as well as, either...or, neither...nor.如: I like Benz, but I do not have enough money to buy it.
(3)主从句
顾名思义，主从句就是那些不仅包含主句，而且还包含一个或者多个具有修饰(限定，说明)作用的从句。作为句子成分，有修饰、限定或者说明作用的主谓结构句为从句；被从句修饰的部分所在的主谓结构称为主句。
如: He hurt his back wh en he fell.其中，he hurt his back是主句，而when he fell是(状语)从句。
b)从句
从句是指在一个大的完整的句子中具有修饰，说明或者限定作用的完整主谓结构。从句可能修饰某个词，甚至是整个句子。除了that和which可以省略以外，所有的从句都有引导词，而且都是陈述语序(而非倒装或者疑问语序)。从句可以分成以下6种:
(1)主语从句
Whether or not she will go is up to her to decide. It was known long ago that air has pressure.(这里，it作形式主语)
(2)宾语从句
Do you think it necessary that we start righ t now?
(3)表语从句
My suggestion is that you should prepare fo r the grammar before you take the tes t.
(4)同位语从句
There i s no probability that he will fail in the TOEFL.
(5)定语从句
定语从句可分为限定性定语从句和非限定性定语从句。
①限定性定语从句
限定性定语从句与被修饰部分的关系紧密，不可或缺。若把该从句去掉，会使主句语义不完整。如: Do you know the man who is smoking over there?
②非限定性定语
从句非限定性定语从句只是用来对被修饰部分作补充性的说明，可有可无。如: Prof essor Robert, whom you met last day, comes from University of Chicago.
(6)状语从句
①时间状语从句
引导词有after, as, as long as, as soon as, before, by the time, each time, every time, hardly...when, hardly...before, no sooner...than, now t hat, once, since, the instant, the moment, till, until, when, whenever, while如: Once you know the grammar rule, you will do well in the grammar section of TOEFL.
②地点状语从句
where, wherever如:swheresthere's a will there's a way.
③原因状语从句
as, because, considering that, for the reason that, not that...but that, in that , now that, since如: Since you are leaving, I get to do it myself.
④结果状语从句
so, so...that, such...that如: He didn't wor k hard, so that he failed in the TOEFL.
⑤目的状语从句
for that, insgroupsth at, so that如: We set out early insgroupsthat we might arrive in time.
⑥比较状语从句
than, as, the more...the more如: The bridge was completed earlie r than we expected.
⑦让步状语从句
although, as, even if, even though, howev er, in spite of the fact that, no matte r, though, whatever, whether如: Thoug h they are poor, they are always neatly dressed.
⑧条件状语从句
as far as, a s long as, but that, if, if only, in case, on condition that, once, only if, on ly that, provided that, so far as, so long as, suppose, unless如: If you ask me, I will help you.
⑨强调状语从句如: It was the TOEFL that you will take.
c) Runs-on句子(包含两个或多个错误连接的独立句子)
如：Current insurance practices are unfair they discriminate against the pe ople who need insurance most.你有两种办法修改run-on句子.第一个办法很简单，直接将两个独立的句子中的逗号改成句号。第二种办法是根据句子的意思用适当的连接词将这些独立的句子连接起来。这种办法比较常用，而且有效。
正确: Current i nsurance practices are unfair, in that they discriminate against the people who need insurance most.
这里，导致run-on句子的是副词however, nevertheless, fur thermore, likewise和t herefore等的误用。
RUN-ON句子: Current insurance prac tices are discriminatory, furthermore they ma ke insurance too expensive for the poor.
正确: Current insurance practices are discriminatory. Furthermore, they make ins urance too expensive for the poor.
B.例题
例题1(1997年8月考题)
Indigo is a vat color,called because it does not dissolve in water.
(A) which it (B) it is (C) but (D) so
这里，句子的主干是Indigo is a vat color。而空格及以后的成分如果没有必要的连词连接的话，不能是完整的主谓结构。所以，我们排除选项B。而无论我们代入A或者C，都不能形成一个符合句法的句子结构。但代入D后，我们发现，空格后成了主句中vat color的同位语，即so指代vat color。选项A如果去掉it的话，which也能起到这种指代作用，但同位语。
例题2(1999年1月考题)
Some snakes lay eggs, but othersbirth to live offspring.
(A) give (B) giving (C) they give (D) to have given
首先分析句子结构。Some snakes lay eggs是一个完整的主谓结构，连词but预示后面应该也带一个完整的主谓结构，所以主语others之后应该填入动词或者助动词当谓语。4个选项中，只有A才能当完整的谓语。B中的giving前缺少助动词，选项C中多了一个主语they，D中的不定式仍然不能单独做谓语。所以，正确答案是A。
例题3(1997年8月考题)
It was in the year 1792
(A) tha t the New York Stock Exchange was founded
(B) founding the New Yo rk Stock Exchange
(C) which year the New York Stock Exchange was founded
(D) the New York Stock Exchange founded
根据我们的经验，这应该是一个强调句型，即it is ...that。其中it是形式主语，指代tha t引导的从句。这里，选项A符合这个句型，将时间状语in the year 1792作为表语是为了强调。即使你对这个强调句型不熟悉或者一时没想起来的话，你也可以根据主谓结构来排除错误的选项。如果将it was in the year 1792看成是一个完整的主谓结构，那么空格里填入的应该是从句或者该主谓结构中每个成分的修饰语。选项B显然不可能是修饰语，当然也不是从句。同理，选项D也不对。而选项C中的which year用法不对，表示年份的时间状语从句应该用in which。
例题4(1999年8月考题)
By means of various types of wind tunnels,sim ulate most of the flight conditions to which an airplane is subjected.
(A) which aeronautical engineers can
(B) aeronautical engineers can
(C) the ability of aeronautical engineers to
(D) aeronautical engineers, being able to
这里，句子的主干应该是simulate most of the flight conditions。而介词短语by means of various types of wind tunnels作方式状语修饰主句，定语从句to which an a irplane is subjected修饰名词conditions。而主干的主谓结构缺的是主语，即空格里应该填入能充当主语的成分。很明显，4个选项中只有B填入空格后能使这个"主干"成为一个完整的独立的主谓结构。
例题5 (1999年8月考题)
Bob Stephenson, a biologist in Alaska who studies the Canadian lynx, a type of w ildcat, has learnedfrom studying their trac ks in the snow.
(A) how lynx hunt (B) lynx hunt how (C) how hunt lynx (D) lynx how hunt
首先，分析句子结构。其中，a biologist in Alaska who studies the Canadian lynx是B ob Stephenson的同位语，而a type of wildcat是the Canadian lynx的同位语。句子的主干是Bob Stephenson has learnedfrom studying their tracks in the snow，该主干中可谓是主谓齐全，填入空格内的应该是及物动词learn的宾语。浏览以下选项，我们发现它们之间的区别在于how，lynx和hunt三个单词的顺序排列。我们知道，how是疑问代词，lynx是名词(一种野猫)，而hunt是动词(打猎，寻食)。这样，根据句意我们可以排除选项B和D。对于选项C，如果要表达"怎么打猎野猫"，应该在how之后加上介词to，但这里没有。所以只有选项A符合这个空格，而且其后的代词their也预示了lynx是复数形式，所以动词用复数形式，即hunt。
例题6(2000年1月考题)
Protein digestion begins in the stomachends i n the small intestine.
(A) while (B) and (C) how (D) because
这里，空格内需要填入一个连词。4个选项中，D中的because后只能带完整的主谓结构，它显然不符合这个空格。选项C的how有两种用法，一个是后面带完整的主谓(或倒装)结构，另外一个是带不定式(how to do sth)。所以它也不适合这个空格。而选项A中的while之后要么带完整的主谓结构，要么是动名词或者介词短语，其后不能带单数的动词ends(当然也不能带end)。所以，A也错。只有B中的and填入空格中才能形成一个符合句法的句子，即两个谓语动词共享一个主语。
例题7(1997年8月考题)
During the course of its growth, a frog undergoes a tru e metamorphosiswith fishlike larval stage.
(A) begin (B) began (C) beginning (D) is begun.
这里，During the course of its growth做时间状语，句子的主干是a frog undergoes a true metamorphosis。空格内填入的不是句子的主干，而应该是定语或者状语。选项A，B和D都只能做谓语，所以他们都不对。只有选项C中的beginning这个分词才能做定语或伴随状语。当然，如果选项B中的began改成begun，或者选项D中的is去掉，他们也能成为正确答案。
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