He pretended when his mother stepped into the room..
A. to study
B. studying
C. to be studying
D. to have studied
网友回答
A. to study
B. studying
(答案→)C. to be studying
D. to have studied
解析：考查不定式用法。不定式的一般式to do说明该动作在谓语动词之后发生；进行时to be doing表示两者同时发生；to be done表示被动；句意：当他的妈妈走进房间的时候，他假装在睡觉。根据句意说明两个动作同时发生，故使用不定式的进行时。故C正确。
考点;考查不定式用法