Question

After years of research, he found the key ____ differences between species.

A．to explain

B．to explaining

C．of explaining

D．explaining

Answer 1

B

试题分析：考查动名词做宾语：the key“关键”后面接to doing做定语，因为to是介词，所以接动名词，句意：多年的研究后，他发现解释物种间差异的关键。选B。
点评; 英语中有些动词短语中的to是介词只能接动名词做宾语，如get down to doing，pay attention to doing，be used to doing，prefer doing to doing等平时要加强记忆。