The main verbs of obligation are; MUST, HAVE TO, SHOULD. The past of have to / has to is had. Must is for personal obligations. Have to is for general obligations.
- You must stop here.
- You have to wear a
seatbelt when you drive.
- You must answer at least one question.
- You should call Mary. I know she misses you a lot.
- She looks sick. She should go home.
- I must do some work.
- You shouldn’t have smoked.
- I have to return the book now.
- I had to wear a school uniform when I was a child.