(Use to where necessary "to" complete the sentences) 1.Have you ever

1. Have you ever seen fish jump?
2. How can you make a child learn to be polite?
3. We all want you to be very happy.
4. Yesterday I heard someone say that the weather was going to change.
5. Ill let you go to the cinema if you are good.
Инфинитив употребляется без частички "to":
- после модальных глаголов (не считая to be to, to have to, to ought to); 
- после глаголов to let, to make;
- в сложном добавленьи после глаголов восприятия (to see, to hear, to feel, to watch etc.);
- после выражений: would rather, had better.