有的同学一看到先行词是表示时间、地点、原因的名词，就认为一定要用关系副词，其实也一定。在此情况下，还要看关系词在定语从句中是用作什么成分，若是用作状语，则用关系副词，若不是用作状语(如用作主语、宾语等)则不能用关系副词，而用关系代词。比较：

This is the factory where I want to work. 这就是我想工作的工厂。(work为不及物动词where在从句中用作状语)

This is the factory that I want to visit. 这就是我想参观的工厂。(visit为及物动词，that用作visit的宾语)

The reason why he can’t come is that he is ill. 他没来的是因为他病了。(come为不及物动词，why在定语从句中用作状语)

The reason that he put forth is very important. 他提出的理由很重要。(put forth为及物动词，that在定语从句中用作其宾语)

六、因逗号误判which

有的同学一看见逗号，就以为一定要选which而不选that，但问题是有时根本就不是定语从句：

(1) If a book is in English, _____ means slow progress for you.

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

(2) When I say two hours, _____ includes time for eating. (D19/541)

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

【分析】以上两题均应选that，而不能选which，因为它们根本不是定语从句。之所以选that，是因为句中已有if和when引导的状语从句，逗号后为主句，that为主句主语。

七、混淆which与whose

两者在定语从句中都可用作定语，区别是：whose 的意思相当于 one's，而 which 的意思则相当于 that 或 this。比较：

(1) This is Mary, whose [= and her] father we met last week.

(2) Call again at 11, by which time [= and by that time] the meeting should be over.