否定句 主语+didn't use to+动词原形
一般疑问句 Did + 主语+use to+动词原形
特殊疑问句 特殊疑问词+ did + 主语+use to+动词原形
He used to go to school on foot.
否定句 He didn't use to go to school on foot.
一般疑问句 Did he use to go to school on foot?
特殊疑问句 How did he use to go to school