Change into passive voice.
1. They should have eaten the meal.
2. I could have done it earlier.
3. We ought to think about it.
4. They must do it./They have to do it.
5. She could have told you.
6. They must show it to you.
7. He may find time.
8. They might have bought that house.
9. She must be offending a lot of people - she's so rude.
10. The kids must have smoked all the cigarettes.