Ответ:
1. This pasta has to be stirred continuously to prevent burning.
2. I have to play the piano for 3 hours.
3. She will have to 3 more books before the next exam in June.
4. You didn't have to eat that if you are not hungry.
5. Last week i had to get up at six a.m. every morning.
6. You don't have to tell the whole story. We had already heard it.