What did you hear last night?" "I seemed someone knock at the door."

问题描述:

What did you hear last night?" "I seemed someone knock at the door."
A hear
B.to have heard
C.to hear
D.having heard

答案是B.因为seem 后跟不定式,在这里要用不定式的完成式,表示的是hear所表示的动作发生在谓语动词seem 之前.