4.I have bought three ballpoint pens，none of　　writes smoothly.

解析：先行词是物three ballpoint pens，前有介词of，故只能用which。

答案：which

3.I have finished reading all the books　　were borrowed from the school library.

解析：先行词是物the books，且有all修饰，只能用that。

答案：that

2.The man about　　you told me the other day turned out to be a thief.

解析：先行词是人，前有介词about，故用whom。

答案：whom

1.The weather was very sunny the following day，　　was what we had expected.

解析：本题用which代替前面整个句子，引导非限制性定语从句。

答案：which

32.It's beyond doubt 　　 that man will lag behind (落后)in the race.

解析：此为that引导的同位语从句，在抽象名词doubt后起补充说明作用，that不能省略。注意：that man中的that起修饰man的作用，指“那个人”，而不是引导词。

答案：that

31.The child is fat.That's 　　he has a sweet teeth(爱吃甜食).

解析：此为because引导的表语从句。That's because...那是因为……。

答案：because

30.The reason 　　 he was absent was 　　 he wasn't interested　 in the meeting.

解析：此为why引导的定语从句以及that引导的表语从句。先行词是the reason，表示原因，故用why；在表语从句中，主语是reason或cause时，引导词要用that，不能用because。

答案：why；that

29.We should help 　　 is in need of our help.

解析：whoever在此为复合关系代词，集先行词和关系词于一体，相当于anyone who。

答案：whoever

28.　　 is likely that we can bridge the generation gap.

解析：此为that引导的主语从句。that从句作主语时，常用it作形式主语。It is likely that...很有可能……。

答案：It

27.　　we'll go camping tomorrow depends on the weather.

解析：此为whether引导的主语从句。当主语从句放于句首时，只能用whether，不能用if。

答案：Whether