when did you do that 中do 为什么用原形不用过去式?

题目

when did you do that 中do 为什么用原形不用过去式?

答案

you did that when这个是这句话的原来位置
转换成问句 be动词或助动词要提前
所以用did you do
did就是do 的助动词形式
比如：i had lunch at 8 o'clock
转换：did you have lunch at .