问题补充:
When I went to their house, there was no light on. They at home.
A. can’t be
B. couldn’t be
C. can’t have been
D. mustn’t have been
答案:
A. can’t be
B. couldn’t be
(答案→)C. can’t have been
D. mustn’t have been
解析:句意:当我到达他们家的时候,没有灯光。他们不可能在家。can’t have been不可能发生了某事,情态动词表示推测,用于对过去发生的事情的否定推测,故选C