I don't know .Did Jack finish his homework?(改宾语从句)

问题描述:

I don't know .Did Jack finish his homework?(改宾语从句)
I don't know _______ Jack finished his homework.怎么改?为什么?

用if
if引导的从句表示“是否……”
whether有两种用法,和or not的话是不能直接放在一起的
用whether的话全句应该是
I don't know whether Jack finished his homework
或者在句末加个or not