am ,is ,are是不是都系动词?

如果am ,is ,are 后面跟名词或者形容词,它们都是系动词。例如：I am a teacher 。He is a student 。They are happy 。如果跟动词ing 形式,它们都是助动词。例如：She is singing 。I‘m flying a kite 。They are playing football 。