As it happens vs as we know

試看這兩句：

1. He is an American, as we know from his accent.

2.As it happens, we probably won't have all that much time for a holiday, though.

有何分別？

分別在於， 第一句的as ,是relative pronoun, 第二句的as, 是conjunction.

其他 作 relative pronoun 的 as,的子句：
as you may have heard, as you may remember

其他as作 conjunction的子句:   as I see it ， as it appears, as I see it