as for

1. 至于; 关于

As for my past, I'm not telling you anything.

关于我的过去, 我什么都不会告诉你。

as if

1. 犹如; 好像

She treats him as if he were a stranger.

她待他如陌生人。

as though

1. 犹如; 好像

He treats his elder sister as though she were a stranger.

他待他姐姐如陌生人。

as to

1. 至于; 关于

As to that, they haven't decided yet.

关于那一点, 他们还未作决定。

as yet

1. 迄今为止

We have received no answer from him as yet.

我们至今还没得到他的答复。