Réponse :
1) You must obey the law
2) you should write her a letter
3) May/Can I smoke ?
4) You must not drive on the right in Great Britain
5) It may/might rain this afternoon
6) How can I contact you ?
7) You should not have drunk too much
8) She looks beautiful, she might be a model
9) She must be more than thirty, she looks young
10) Who's that man over there ? He must be the you were waiting for
Exercice 2
1) can, can't
2) can
3) can
4) can't
5) can
6) can't
7) can
8) can, can
9) can't
10) can't
Exercice 3
1) can
2) could
3) couldn't
4) couldn't
5) could
6) couldn't
7) couldn't