2.used to的否定式与疑问式

(1)used to的否定式是usedn't to，didn't use to，didn't used to或used not to。

He usedn't/didn't use/didn't used/used not to smoke．

他以前不常吸烟。

(2)used to的疑问式是used．．to?did．．used to?或did．．use to?

Used he to live in the country?/Did he use(d)to live in the country?

他以前住在乡村吗?

(3)used to附加的疑问式是didn't．．?did．．not?usedn't．．?或usen't．．?

He used to smoke，didn't he?/did he not?/usedn't he/usen't he?

他过去常抽烟，是吗?

They usedn't/didn't use/used not to like opera，did he?

他们以前不喜欢歌剧，不是吗?

There used to be some trees in this field，usedn't there?/usen't there?/didn't there?

过去在田里有几棵树，是不是?

提示：

有人认为didn't used to是非标准用法。