I don't know whether you happen_____ but I'm going to study i n the US A.to have heard 为什么?

问题描述:

I don't know whether you happen_____ but I'm going to study i n the US A.to have heard 为什么?

happen 后面加动词要用happen to do sth.表示碰巧做某事,现在完成时表示事情已经发生并对现在仍有影响.