The professor could hardly find sufficient grounds_____his arguments in favor of the new theory.

A.on which to base

B.which to base on

C.to base on

D.to be based on

答案：

D

解析：

[译文]教授几乎找不到足够的理由作为其论据的基础以支持这种新理论。[题解]base sth.on…为固定搭配，[D]中的介词on放于指代sufficient grounds的which前，正常语序应是 to base his arguments on sufficient grounds，因此[D]正确。