那男孩高兴地跳个不停。

d.表示两个动作是同一动作

He who helps others is helping himself.

帮人就是帮自己。

If you insist on doing it, you are doing a foolish thing.

如果你坚持做这件事，你就是在干傻事。

e.be动词的进行时态

be动词一般不用于进行时态。但有时可用“am, is, are + being +形容词”结构表示暂时或故意如此。

The boy is being naughty.这孩子有点儿淘气。

I don't think you are being fair.

我认为你不公平。

He is being modest.

他现在很谦虚。

比较：

You are not polite.

你不讲礼貌。（一贯如此）

You are not being polite.

你可有点儿不礼貌了。（暂时的现象）

3．不用进行时态的动词

①表示状态的动词

这类动词有seem, look, appear, have, belong to, own, hold等。

This backpack belongs to me.

这背包是我的。

He seems rather angry with you.

看起来他很生你的气。

②表示知道、信念、理解、推测、怀疑、希望等含义的动词

这类动词有know, remember, understand, see, think, believe, suppose, hope, doubt