mustbedoing是什么时态

must be doing是正在进行时态，must be doing表示一定在做什么；

例如

But he must be doing it very well.

但是他应该工作得很出色。

I know you must be doing well.

我知道你一定过的很好！

If they are nervous, you must be doing something really new!

如果他们神经紧张，那你必须做一些真正新的东西！

He must be doing some cold calculating just now.

刚才他肯定是在冷静地计算着。

He must be doing something great.

他一定做了什么了不起的事。

You must be doing something right.

你肯定做了什么好事儿了吧。