描述主语是什么,什么样子,什么职业等,也就是动词后面跟的是一些名词,形容词,介词短语类词时要用be动词.如：Is she a student?
Are they old
Is Mike
Is our teacher in the classroom
如果描述主语的动作时,也就是后面还要跟动词时,这时用do动词.
如：Do you often go to school at seven?
Does Lucy usually go to see her grandma