Khẳng định:

I used to go swimming.

He used to smoke.

I used to eat meat before becoming a vegetarian.

Phủ định:

I didn’t use to go swimming.

He didn't use to smoke.

I didn't use to eat meat before becoming a vegetarian.

Nghi vấn:

Did you use to go swimming?

Did he use to smoke?

Did you use to eat meat before becoming a vegetarian?