How can you be certain of this?

你怎么能这么确定？

My mechanical and reptilian logic are certain of it.

我的机械和爬虫逻辑相当确定。

Yes, I am. And how can you be certain of this?

是的 你何以确定？

They were both English; my young friend was certain of this.

他们都是英国人。这一点我这位年轻的朋友十分肯定。

" Oh, I'm certain of it. Might I see your lute" ?

" 噢，这当然啦。我能瞧瞧你的琵琶么？"

I can't be certain of what time I left the office.

我不能肯定我是什么时候离开办公室的。

The telling clause here is Unless he is certain of doing well.

这里的关键部分是“除非作者确认自己写得很好”。

Still, no one is certain of the actual identity of the model.

不过，没有人能确定这位模特的真实身份。

I've put water into the desert because I am certain of success.

我把水引向沙漠中因为我确信一定能成功。

" Dead, he's dead, you are certain of that" ?

" 死了，他死了，你确定？"