问题补充：
Tom pretended it；but in fact，he knew it very well.
A. not to listen to
B. not to hear about
C. not to have heard about
D. not to be listening to
答案：
A. not to listen to
B. not to hear about
(答案→)C. not to have heard about
D. not to be listening to
解析：pretend not to have done假装没做过某事；pretend to be doing sth.假装正在做某事；pretend to do sth.假装做某事。由he knew it very well可知，应选C项。
