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
从选项中可知，定语从句中有一个插入语we think，而插入语一定是紧跟在引导词之后的。sth．be of+n．＝sth．be+adj．(此结构中的名词和形容词是同源的)，因此选B项。从句若去掉插入语，就是which are of much help“有很大帮助”。这里从句的谓语动词用复数，说明将experiments看作了先行词，也可以将主句整句话看作先行词，那么从句谓语动词就应该用is了。