be doing是什么時態?

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

　　如果你拿不準是否應進行這種鍛煉，咨詢一下醫生好了。

　　What can they be doing?

　　他們究竟在干些什么呢？

　　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.

　　我已開始詳細安排下周要干的事兒了。

　　Anyone could be doing what I'mdoing

　　我在做的事，誰都可能正在做。