2,2, Mum used to drink coffee.

3,3, We used to eat meat.

4,4, People used to drop rubbish.

5,5, All the energy used to come from fossil fuels.

6,6, There used to be more animals. 

7,7, We didn't use to do exercise.

8,8, I used to watch TV.

≈≈≈≈≈≈

Cấu trúc used to:

(+)(+) S + used to + Vnguyên thể

(−)(-) S + didn't + use to + Vnguyên thể

(?)(?) Did + S + use to + Vnguyên thể?

2.used to drink coffee.
3.used to eat meat.
4.  used to drop rubbish.
5.  used to come from fossil fuels.
6. used to be more animals.
7. used to do no exercise.
8. used to watch TV