有许多试题，由于同学们对句子结构分析不对，尤其是对句中的逗号判断失误，从而导致一些想当然的错误。试举几例：
 
1. If a book is in English, _____ means slow progress for you.

A. as        B. which      C. what        D. that

此题容易误选 A或B，想当然地根据空格前的逗号认为这是非限制性定语从句。这样分析的同学，主要是忽略了前一句句首的B if。其实此题应选D，逗号前是一个条件状语从句，逗号后是该状语从句的主句，that 在此代表前文所述的情况，用作主句的主语。同样地，下面几题也应选 that，而不选 which：

(1) If he’s only interested in your looks, _____ just shows how shallow he is.

A. as        B. which      C. what        D. that

(2) If you want to go, _______is quite all right with me.

A. that       B. which       C. and it         D. so

(3) When I say two hours, _____ includes time for eating.

A. as        B. which      C. what        D. that

(4) If you want a double room , _____ will cost another ￡15.

A. as        B. which      C.  what       D. that

(5) If you have the money, _____ will be OK.

A. as        B. which      C. and it        D. that

下例也选 that 而不选Y: 'Times New which，其中 that 表示“那”：

Unless I’m very much mistaken, ______ is my watch you’re wearing!

A. as        B. which      C. what        D. that


2. Not far from the school there was a garden, _____ owner seated in it playing chess with his little grandson every afternoon.

A. its       B. whose       C. which      D. that

此题很容易误选B，许多同学想当然地认为句中逗号后是一个非限制性的定语从句，whose 在定语从句中用作定语修饰其后的名词 owner。此分析从表面上看，似乎天衣无缝，但实质上是错的，原因是空格后根本不是一个句子，因为它没有谓语。尽管句中有两个动词，但它们都是非谓语动词。也许有的同学会问，其中的 seated 不可用作谓语动词吗？不能。因为seat 用作动词时，它总是及物的，其后要么接宾语，要么它就用于被动语态，所以若在 seated 前加上助动词 is，则可以选择B（当然若将 seated 改为 seated sitting，也应选择B）。所以此题最佳答案选A。请再看一个类似的例子：

(1) He wrote a lot of novels, many of _____ translated into foreign languages.

A. it      B. them       C. which     D. that

(2) He wrote a lot of novels, many of _____ were translated into foreign languages.

A. it      B. them       C. which     D. that

第(1)题应选B，而不能选C，是因为句中的 translated 是过去分词(非谓语动词)，若选C，则该从句无谓语；第(2)题应选C，因为句中有谓语 were translated。再请看下面一例：

(3) He wrote a lot of novels, and many of _____ were translated into foreign languages.

A. it      B. them       C. which     D. that

此题与上面的第(2)题不同，两句间多了一个并列连词and，说明这是一个并列句，故应选B，则不能选C。

请做做以下三题(答案均为B)：

(1) There I met several people, two of _____ being foreigners.

A. which     B. them       C. whom      D. that

(2) There I met several people, two of _____ were foreigners.

A. which     B. whom       C. who      D. that

(3) There I met several people, and two of _____ were foreigners.

A. which     B. them       C. whom      D. that

3. _____ is known to everybody, the moon travels round the earth once every month.

A. It                B. As              C. That           D. What

此题很容易误选 A，认为此处应填一个形式主语，况且 It is (well) known to … 也是一个常用句型，读起来也很上口，但是选A错了。同学们仔细想想看，假若选 A，空格处填一个形式主语(it)，那么其后就应有一个真正的主语，但事实上没有。但是若句中的逗号改成 that，则只能选 A，that 便成为一个引导主语从句的引导词。此题的最佳答案是 B，as 引导的是一个非限制性定语从句，可置于主句前(常译为“正如”)或主句后(常译为“这一点“”)，句意为“正如大家所知，月球每月绕地球转一周”。

4. He is always really rude, ______ is why people tend to avoid him.

A. that            B. it             C. this            D. which

此题容易误选 A，因为 that’s why … 是一个常用表达，同学们极易受此影响而选错，当然若此句的空格前有连词 and 或其前的逗号改为分号，则完全可选that（分别构成并列句和两个独立的简单句）。此题的最佳答案是 D，句子后半部分为一个非限制性定语从句，which 指 He is always really rude. 另外请比较以下两题（注意连词的有无）：

(1) He had a lot of friends, none of ______ could lend him any money.

A. whom         B. them           C. which          D. who

(2) He had a lot of friends, but none of ______ could lend him any money.

A. whom         B. them           C. which          D. who

第(1)第题选A，none of whom could … 为非限制性定语从句；第(2)题选B，由于句中有并列连词 but，整个句子为并列句。

5. He wrote a lot of novels, none of ______ translated into a foreign language.

A. them              B. which          C. it              D. what

同学们看了上面一题的分析后，也许会毫不犹豫地认为此题应选 B，理由是none前没有并列连词 and 或 but，其实这次又错了。此题的最佳选项应是A，其实这次又错了。此题的最佳选项应是，注意此句与上面一句有着本质的不同，即此句的 translated 不是谓语，而是一个非谓语动词（过去分词），所以逗号后面其实不是一个完整的句子，而是一个独立结构。假若在 translated 前加一个助动词 was，则此题应选 B(which)，构成一个非限制性定语从句。所以做这类题要特别小心，千万不要想当然，更不要受定势思维的影响。又如：

(1) I met several people there, two of ______ were foreigners.

A. whom        B. themA.           C. who            D. which

(2) I met several people there, two of ______ being foreigners.

A. whom        B. them          C. who            D. which

第(1)题选A，two of whom were foreigners 为非限制性定语从句；第(2)题选B，two of them being foreigners 不是一个完整的句子，因为句子没有谓语，而只有非谓语动词 being。