1、Did you do your homework yesterday?（用at this time yesterday改写）
Were you doing your homework at this time yesterday?
昨天这时候你在写作业吗?
这是改为过去进行时态.
2、I have been to the Great Wall twice.（对twice提问）
How many have you been to the Great Wall?
你去过长城几次了?
这是对次数提问.