1. 现在进行时：表示现在正在进行的动作或现阶段经常发生的动作，由am/is/are + V-ing构成，如：
　　　　What are you doing? I'm washing my clothes.
　　　　Tom is getting on well with his studies.
　　　　They are always complaining.

　　2. 过去进行时：由was/were + V-ing构成，表示过去某时正在进行的动作，如：
　　　　What were they doing at nine o'clock last night?
　　　　They were watching a TV play.

　　3. 将来进行时：由will + be + V-ing构成，表示将来某时要发生的事，如：
　　　　I will be doing my homework this time tomorrow.
　　　　They will be sitting in the cinema at seven tomorrow evening.