The company doesn't have to / mustn't do any more trials on the vaccine because it has been declared safe.

I think she's wrong to make promises which she doesn't keep. She .......... make promises which she doesn't keep.

You _________ make more of an effort in class.

It is against the rules to talk in here. You ______ do it!

You ___________ call Maria. I know she misses you a lot.

You mustn't / needn't look at other students' work.

You don't have to / mustn't stand on the desk. Otherwise, you'll break it.

You ________ do exercise every day. It's good for you!

It was wrong of them to use the machine without asking for permission first. They .......... have asked for permission before using the machine. SHOULD

You _________ to do your homework or study, it's summer!

I _________ study this weekend. It's my obligation as a student.

You can give the tour guide a tip but it's not necessary. You ..............give the tour guide a tip.

You _______ tell anyone what I've just told you. It's a secret.