I happened (cover)the event then 括号里填正确形式,怎么填?为什么?

题目

I happened (cover)the event then 括号里填正确形式,怎么填?为什么?

答案

碰巧[W][+to-v]
I happened to sit by her in the cinema.
在电影院我碰巧坐在她旁边.
因而应填to cover