Choose the correct options to complete the sentences

1. At night, it [can|must]
   get very cold in the desert.
2. She was so astonished that she [shouldn't|wasn't able to]
   say a word.
3. [May|Should] I come in?
4. People having agoraphobia usually [can't|mustn't]
   use the subways.
5. It's so cloudy tonight. It [may|have to]
   rain at night.
6. Aunt Polly's brought us some fresh buns, so you [don't have to|mustn't]
   buy pastry today.
7. You [may|must]
   keep silent in the library.
8. Jim [has to|can] work harder to pass the entry test.
9. You [can't|shouldn't]
   buy small toys for infants — they can swallow them or choke.
10. I [need to|may]
    practise more often to speak fluently.
11. You look pale. You [must|ought to]
    get outside and have some fresh air.
12. Don't stay behind a horse. It [can|must]
    get scared and kick you.