A-A+
-- I saw Mary in the library yesterday. -- You
问题详情
-- I saw Mary in the library yesterday. -- You __.her, she is still in hospital. A．mustn"t have seen B．could not see C．can"t have seen D．must not see
参考答案
正确答案：C
情态动词must作为推测时，不能用于否定式，它的否定式是can’t，故排除选项A、D。虽然问句用了过去式，但回答时强调的是结果，故选择完成式。
