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?