Question

bobo __hard,otherwise he___ in this exam

A.can't have worked ;wouldn't have failed
B.can't work;wouldn't have failed
C.mustn't have worked;wouldn't fail
D.must have worked;would fail

A man answered the phone.I suppose it was her husband.
It__ her husband. He has been dead for ages.
A.mustn't be B.mustn't have been
C.couldn't be D.couldn't have been.

he___ be in hospital.I met him in the library only a moment ago
A.can't B.mustn't C.may not D.shouldn't

Answer 1

1. A
原因：bobo（）用功，否则他（）考试。意思先猜一下，他要再用功些，否则他就过不了考试。或者是：他可能没有好好用功，否则他不会过不了考试的。
B错在，后面用了虚拟，前面没有用语法上不对。
C的意思是，他不可以再用功，否则他不会通不过考试的，wouldn't fail双重否定，表示通过考试，意思和逻辑上是错的，所以不对。
D- must have done，是肯定在过去做了什么事的意思，他肯定用功了，否则他会“would fail”没过考试，逻辑上错误，也不对。
A：can't have done，不可能过去做了什么，前半句的意思是他不可能之前用功了，otherwise he wouldn't have failed，否则他不会失败。意思、语法和逻辑都正确。

2. C
原因：一个男人接了电话，我猜可能是她老公。它（）她老公，死了几年了。（）处肯定应该是（不可能），整个句子是过去时，表示过去不可能用could not be

3. A
原因：can't 是不可能的意思（现在时），mustn't是不允许的意思，本句意思是：他（不可能）在医院里，我几分钟前刚在图书馆里遇见他，所以用can't，而不是mustn't。may not-可能不是，但因为刚碰到，所以很肯定不可能用can't，shouldn't是不应该的意思，只有A正确。

Answer 2

1. C.mustn't have worked;wouldn't fail
2. C.couldn't be
3. B.mustn't

Answer 3