一个选择题，请帮我分析下，谢谢

来源：百度知道 编辑：UC知道 时间：2024/07/07 22:38:14
31.______that the earth was flat?
A.used it to be thought B. does it used to thought
C.do it used to be thought D.used to it be thought

选哪个才对啊？为什么呢？请帮我分析下，谢谢了

A.used it to be thought
陈述句为 it used to be thought that the earth was flat
转换成问句 可有两种方法
一是把used提前 成为used it to be thought that the earth was flat？
二是 就used的过去式提问 成为 did it used to be thought that the earth was flat?
加油 好好学