▲as it happens 和 it happens that…都可以表示“碰巧”，它们在意思上没什么区别，在用法上，as it happens 可用于句首或句末。如：
As it happens, I have my notebook with me. 碰巧我带着笔记本。
I saw him in the street yesterday, as it happens. 我昨天碰巧在街上见到了他。
▲而 It happens that…只能用于句首（happen 前有时可用 so, just 等修饰）。如：
It (so) happened that she was out when he called. 他打电话时，她碰巧不在家。
It (just) happened that he had read the book. 他碰巧读过那本书。