8、先行词表示地点时,有时用where,有时用that, which来引导定语从句.这时要根据从句的谓语动词是及物还是不及物，是及物的就用that(which)，否则用 where。

例如：This is the factory where we worked last year.

This is the factory that (which)we visited.

7、先行词被the only, the very, the same, the last 修饰时，只能用that。

例如：He is the only person that attended the meeting.

6、先行词被序数词或形容词最高级所修饰，只能用that。

例如：This is the most exciting film (that) I have ever seen.

5、先行词是不定代词:all, few, little, much, something, nothing, anything等，只能用that。

例如：That’s all (that)I want to say.

4、that在定语从句中可以指人或物,在从句中作主语或谓语动词的宾语.但不能放在介词后面作介词宾语。

例如：The letter that I received was from my father.

3、关系代词which在非限制性定语从句中不能放在句首,as既能在句首也能在句中.

2、关系代词whom, which, that 在限制性定语从句中作动词宾语或介词宾语,而该介词又位于从句末尾时,经常省略,但as一般不省略.

1、关系代词在从句中作主语时,从句的谓语动词的人称和数必须和先行词保持一致.

50. No sooner had we got to the top of the mountain ______ it began to rain .

A. when　　 　　　　 B. as　 　　 　　　　　　　　　　 C. than　 　　　 　　　　　　 D. while

49. It must have rained last night , ______the ground is still wet.

　 A. so　　 　　　　　　　 B. for　　 　　　　　　　　　　 C. or　　 　　　　　　　 D. but