Question

The astronaut did many experiments in the spaceship, ________ much help for knowing space．

1. A.
   which we think it is
2. B.
   which we think are of
3. C.
   of which we think is
4. D.
   I think which is of

Answer 1

B
從選項中可知，定語從句中有一個插入語we think，而插入語一定是緊跟在引導詞之后的。sth．be of+n．＝sth．be+adj．(此結構中的名詞和形容詞是同源的)，因此選B項。從句若去掉插入語，就是which are of much help“有很大幫助”。這里從句的謂語動詞用復數(shù)，說明將experiments看作了先行詞，也可以將主句整句話看作先行詞，那么從句謂語動詞就應該用is了。