题目内容：

used to do改为否定句
Jack used to live in a small village with his grandpa.改为否定句
印象里不是应该在used和to之间加not吗?
为什么答案是didn't use to

优质解答

used to do 有两种否定形式
1.usedn't to do （used not to do）
2.didn't use to do
疑问也是两种
Used……?
Did……?
所以都可以,不过didn't use to 更加常见