The rules
- After a modal verb, use the base form of the verb: She can swim.
- Modals never add -s and are not followed by to (except ought to): He must wear a helmet.
- Use a modal plus have plus the past participle to talk about the past: You should have called me.
- Must have shows you are sure about the past, and might, may or could have show it is possible: The road is wet, so it must have rained.
- Had better and would rather are followed by the base form: You had better leave now, and I would rather walk.
- Have to is used for obligations in any tense, since must has no past form: Yesterday we had to wait.
- Mustn’t means something is not allowed, but don’t have to means it is not necessary: You don’t have to pay, but you mustn’t touch.
This time: 0 right, 0 wrong