1 . I ________ have been more than six years old when the accident happened.

A．shouldn’t

B．couldn’t

C．mustn’t

D．needn’t

2 . The streets are all dry. It ________ during the night.

A．must have rained	B．can’t have rained
C．couldn’t rain	D．shouldn’t have rained

3 . But for their common interests, they_____ cooperated so smoothly in the investigation of the case.

A．could have

B．will not have

C．could not have

D．have not

4 . He___ have attended the meeting this morning. He has been staying at my home for a whole day.

A．can’t

B．mustn’t

C．shouldn’t

D．needn’t