关于过去时和现在完成时

题目

关于过去时和现在完成时
1Oh It's you I ___(not know) you___(Be) here.
2It's dangerous to swim here.Look at the sign.
I ___(not notice) it.Thanks for telling me.
为什么.怎么区分过去时和现在完成时?说得详细些.

答案

1.Oh It's you,I didn't know you are here.didn't know 过去时,表示过去的动作,已经结束,之前不知道你在这,后面的you are here表示事实,用现在时,况且人家现在确实还在那儿嘛呵呵2.It's dangerous to swim here.Loo...