有的同學一看到先行詞是表示時間、地點、原因的名詞，就認為一定要用關系副詞，其實也一定。在此情況下，還要看關系詞在定語從句中是用作什么成分，若是用作狀語，則用關系副詞，若不是用作狀語(如用作主語、賓語等)則不能用關系副詞，而用關系代詞。比較：

This is the factory where I want to work. 這就是我想工作的工廠。(work為不及物動詞where在從句中用作狀語)

This is the factory that I want to visit. 這就是我想參觀的工廠。(visit為及物動詞，that用作visit的賓語)

The reason why he can’t come is that he is ill. 他沒來的是因為他病了。(come為不及物動詞，why在定語從句中用作狀語)

The reason that he put forth is very important. 他提出的理由很重要。(put forth為及物動詞，that在定語從句中用作其賓語)

六、因逗號誤判which

有的同學一看見逗號，就以為一定要選which而不選that，但問題是有時根本就不是定語從句：

(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】以上兩題均應選that，而不能選which，因為它們根本不是定語從句。之所以選that，是因為句中已有if和when引導的狀語從句，逗號后為主句，that為主句主語。

七、混淆which與whose

兩者在定語從句中都可用作定語，區別是：whose 的意思相當于 one's，而 which 的意思則相當于 that 或 this。比較：

(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.