Complete the sentences with a suitable modal verb. Use must, should, must have, mustn't and shouldn't.
1)You drive on the pavement.It's illagel. 2)You say that. It's not nice.
3)He's not here. He gone out. 4)You eat more vegetables.They're good for you. 5)You be 18 before you can buy alcohol. 6)Boys and girls, you ... hand in your essays by Thursday.​

1) mustn't

2) shouldn't

3) must have

4) shouldn't

5) must

1) You mustn't drive on the pavement. It's illegal. (Mustn't is used to express prohibition or a strong obligation not to do something.)
2) You shouldn't say that. It's not nice. (Shouldn't is used to give advice or express a suggestion about what is the right or best thing to do.)
3) He must have gone out. (Must have is used to express a deduction or a strong belief about something that happened in the past.)
4) You should eat more vegetables. They're good for you. (Should is used to give advice or express a suggestion about what is the right or best thing to do.)
5) You must be 18 before you can buy alcohol. (Must is used to express a strong obligation or necessity.)
6) Boys and girls, you must hand in your essays by Thursday.​ (Must is used to express a strong obligation or necessity.)

Explanation:
1) It is stated that driving on the pavement is illegal, so it is important to use the modal verb mustn't, which expresses prohibition or a strong obligation not to do something.
2) It is mentioned that saying something is not nice, so the modal verb shouldn't is used to give advice or express a suggestion about what is the right or best thing to do.
3) It is indicated that he is not here, so the deduction is made that he must have gone out. "Must have" is used to express a deduction or a strong belief about something that happened in the past.
4) It is mentioned that vegetables are good for health, so the modal verb should is used to give advice or express a suggestion about what is the right or best thing to do.
5) It is stated that a person needs to be 18 before buying alcohol, so the modal verb must is used to express a strong obligation or necessity.
6) The students are being instructed to hand in their essays by Thursday, so the modal verb must is used to express a strong obligation or necessity in this situation.