Choose the correct options

1. Four years ago Mike
   [had to|could|couldn't]
   fix cars, but now he can.
2. Last Thursday Carry
   [could|wasn't able to|didn't have to]
   meet us. She was very busy with her report.
3. [Had to|Сould|Сan't]
   you help me with cooking dinner?
4. When I was a kid, I
   [didn't have to|had to|could]
   go to school. I studied at home.
5. When Mary got into her car she
   [was able to|couldn't|didn't have to]
   drive because it was broken.
6. Students
   [could|were able to|had to]
   pass the exams twice a year.
7. The professor
   [didn't have to|couldn't|was able]
   to explain a new theme to them, but they didn't ask him for help.