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

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

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.

happen
碰巧[W][+to-v]
eg:I happened to sit by her in the cinema.
在电影院我碰巧坐在她旁边。