is, am, are的动词原形是be, 可作系动词,意思为“是”,如:He is young. You are clever. I am a teacher. be还可作助动词(无词意,只帮助构成时态与语态)如:I am answering your question. am answering进行时态;The room is cleaned every day. is cleaned被动语态。而do可以作行为动词,也可作助动词。如:They do their homework every day. do行为动词“做", Do you understand me now? do助动词,帮助构成疑问句。be动词与do的否定:He is not at home. He doesn't do his work every day. 如还有不懂,请给我留言。