do代表动词原形，既能是及物动词，也能是不及物动词。

v.做，干，办(某事);(以某种方式)做;行动;表现;(问询或谈论时用)进展，进行

例句：

Someone might find out, and that would never do.

也许有人会发现，那是绝对不行的。

What sort of person would do a thing like that?

什么人会干那样的事呢？

They think I can't do it, but I'll show them!

他们以为我做不了，我却要做给他们看看！

Keep going like that ─ you're doing fine.

就这样做下去——你做得蛮不错嘛。

What is he doing calling at this time of night?

他干吗这么晚了还打电话？