be doing是什么时态?

If you are in any doubt as to whether you should be doing these exercises, consult your doctor.

如果你拿不准是否应进行这种锻炼，咨询一下医生好了。

What can they be doing?

他们究竟在干些什么呢？

You can't be doing two things at once

不能一心二用。

I have started planning out what I shall be doing next week.

我已开始详细安排下周要干的`事儿了。

Anyone could be doing what I'mdoing

我在做的事，谁都可能正在做。