The professor could hardly find necessary grounds_______his arguments in favour of the new theory.A.to be based on B.to base on C.which to base on D.on which to base选什么?why?

答案为D,原因如下
（1）考点为　介词+关系代词+不定式
（2）首先要明白的短语
　　　 base ..on...　　以。。。为依据，建立。。于。。
　　　 in favor of 　　支持
(3) 原句如果是定语从句的话，那么就是
The professor could hardly find necessary grounds on which he bases
his arguments in favour of the new theory 　
　　　on前面的是主句，后面的是on which引导的定语从句，修饰先行词grounds（n.根据）
这个定语从句转换一下，he bases his arguments in favour of the new theory on
grounds　他把支持新理论的观点建立在某某根据上。　
　　　his arguments in favour of the new theory 中，in后面的部分是定语修饰his arguments
(4) 介词+关系代词的结构常省略为　介词+关系代词+不定式　的结构。所以就成了
The professor could hardly find necessary grounds　　　　
on which to bases his arguments in favour of the new theory 　

(5) 本句的句意为：教授找不到必要的、建立其支持新理论的观点的根据
　　通顺点就是，教授找不到支持新理论的观点的必要根据

本题选D。
on which to base his arguemnets作定语修饰grounds.
in favour of the new theory修饰arguments。
本题考查该结构为：介词+which+不定式，必须存在介词才可以用。
which是关系代词，该结构比较特殊，可以看做定语从句的省略形式。如：
Could you please lend me some money with which to buy a dictionary?

答案选 D.on which to base
句意：这位教授几乎不可能找到必需的理由,以此来支持新学说.
固定短语：base sth on sth.
原句剖析：The professor could hardly find necessary grounds（ on which to base his arguments） in favour of the new theory.划线部分为定语从句,正常语序应该是which he base his arguments on介词提前可以得到on which he base his arguments ,大家都知道宾语从句中what to do=what we should do ,类比可得,此句可改成on which to base his arguments 答案：D

我觉得选择D