Question

John________ such a thing about you．He never speaks ill of you be-hind your back．

1. A.
   can't have said
2. B.
   might not have said
3. C.
   couldn't say
4. D.
   mustn't have said

Answer 1

A
从后一个句子可以看出本句表示的是对过去推测，其语气十分肯定。