例句：1.Did Tom do his home work yesterday?When?回答：I want to know if Tom did his homework yesterday.请问回答中的为什么要过去式did而不用单数第三人称does?
问题描述：
例句：1.Did Tom do his home work yesterday?When?
回答：I want to know if Tom did his homework yesterday.请问回答中的为什么要过去式did而不用单数第三人称does?
答
因为是yesterday的事，tom有没有做作业是昨天的事，即过去的事，用过去式did.
答
因为时间状语是yesterday
答
因为这是个宾语从句 主句是一般现在时 从句该用哪个时态就是哪个时态了 有yesterday所以用一般过去时