Choose the correct options
Modal Verbs: Can, Could, Must, Have To
Модальный глагол can/can't употребляется, чтобы выразить:

• Способность, умения:
  He can swim.
• Разрешение на определённое действие:
  You can use my mobile phone.
• Возможность определённого действия:
  She can buy this shirt online.
• Просьбу:
  Can I go home now?
• Запрет:
  You can't eat sweets unless you have soup for lunch.

Could употребляется для выражения вежливой просьбы.

Could I borrow your dictionary?

Модальный глагол must/mustn't употребляется для обозначения:

• Правил, долга или обязательств:
  Pupils must wear a uniform at school.
• Запрета:
  You mustn't talk loudly in class.

Модальный глагол have (has) to / don't (doesn't) have to употребляется для выражения необходимости (или её отсутствия), обусловленной обстоятельствами.

I have to get up early because my lessons start at 8 o'clock.

You don't have to iron the clothes, I have already done it.

1. You
   [must|have to]
   keep off the grass. It is a rule.
2. Crocodiles
   [can|must]
   swim very fast.
3. The teacher says that students
   [have to|can to]
   study hard before exams.
4. You
   [mustn't|don't have to]
   smoke here. It is forbidden.
5. [Could|Must]
   I borrow your mobile? I have lost mine.
6. She
   [can|has to]
   speak French very well—her mother is a French teacher.
7. You
   [don't have|can]
   to buy this book, I have it at home.
8. You
   [can't|must]
   go for a walk until you mop the floor in your room.