关于base on的用法

Question

The Professor could hardly find sufficient grounds__his arguments in favor of the new theory.
A. to be based on
B. which to base on
C.to base on
D on which to base
选哪个，请一定要说明为什么啊！~

Answer 1

选D...which指代ground...
前面的介词on必须有，因为这里相当于用了base on the ground这个短语..在定语从句中当用which指代了ground, ground前面的on还是应该存在.但这时候自然要加在 which前面，所以变成了on which to base

Answer 2

D。