Помогите, кто знает.

1. Peter was watching a documentary when the phone .....
a) rings b) rang c) have rang

2. We ..... take photos in the museum. It's not allowed!
a) mustn't b) must c) should

3. If you wake up early, you ...... late for work.
a) be b) aren't being c) won't be

4. You ..... all night. You must be exhausted!
a) 've studied b) are studying c) 've been studying

5. They ..... him a car when they find an inexpensive one.
a) were buying b) buy c) will buy