`1` They used to play tennis twice a week.
`to` (-) They didn't use to play tennis twice a week.
`to` (?) Did they use to play tennis twice a week?
`2` I used to go to the gym three times a week.
`to` (-) I didn't use to go to the gym three times a week.
`to` (?) Did you use to go to the gym three times a week?
`3` Tennis used to be a sport for rich people only.
`to` (-) Tennis didn't use to be a sport for rich people only.
`to` (?) Did Tennis use to be a sport for rich people only?
`4` My father used to take me to see soccer games on Saturday.
`to` (-) My father didn't use to take me to see soccer games on Saturday.
`to` (?) Did your father use to take me to see soccer games on Saturday?
`5` He used to buy a new tennis racket.

`to` (-) He didn't use to buy a new tennis racket.
`to` (?) Did he use to buy a new tennis racket?

Cấu trúc: 

(+) S+ used to+ V-inf.

(-) S+ didn't use to+ V-inf.

(?) Did+ S+ use to+ V-inf?

Công thức

+) Khẳng định (+): S + used to + V-inf

+) Phủ định (-): S + didn't + use to + V-inf

+) Nghi vấn (?): Did + S + use to + V-inf?

1. (-) They didn't use to play tennis twice a week.

    (?) Did they use to play tennis twice a week?

2. (-) I didn't use to go to the gym three times a week.

    (?) Did I use to go to the gym three times a week?

3. (-) Tennis didn't use to be a sport for rich people only.

    (?) Did tennis use to be a sport for rich people only?

4. (-) My father didn't use to take me to see soccer games on Saturday.

    (?) Did my father use to take me to see soccer games on Saturday?

5. (-) He didn't use to buy a new tennis racket.

     (?) Did he use to buy a new tennis racket?

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