这句话语法对么?Did you used to borrow books from the school library

呃 全错.
这句的陈述句是 You used to borrow books from the school library.
句中第一个动词是used 转化成一般疑问句应该就used 提问.由于used是过去式,所以一般疑问句应该以助动词Did开头.在一般疑问句中,由于有助动词,其对应的动词应该变为原型.
例:
My father gets up early.转化为一般疑问句为：
Does your father get up early
由于gets是单数形式 一般疑问句的助动词也要是单数形式 所以是does
而gets变为原型get.
所以 正确的应该是Did you use to borrow books from the school library
以下补充摘自我的英语课本：
used to 构成疑问时可借助助动词did或直接将uesd移至主语之前,但后者不常用.例如：
Did you use to see each other?=Used you to see each other?你们过去常见面吗.

Did you used to borrow books from the school library? 这句话正确
DID 和USED TO DO 时态对应
过去常常做某事，习惯于做某事，被用来做某事的区别是什么？
答：used to do sth./ be used to doing sth./ be used to do sth.
1、 used to do...

第二个对，是USED TO 的用法，

其实两个都对。
the first one implies to talking about what had already happened, while the second is referring to what might, could have been, or going to happen.
你想说已经发生的 还是 没有（或者将会）呢？

used to 的意思是 过去常常 用过去时态 前者是正确的