---I think Helen is at home.---No shebe at home for she phoned me from the airport just

问题补充：

---I think Helen is at home.

---No, shebe at home, for she phoned me from the airport just five minutes ago.

A. mustn

B. needn

C. can

D. dared not

答案：

A. mustn

B. needn

(答案→)C. can

D. dared not

解析：句意：我想海伦应该在家里。不，她不可能在家里，因为她刚刚五分钟前还从机场给我打电话了。can’t不可能，用在否定句中表示对事情的强烈的否定推测。故选C