系动词有以下单词：be,is,are,am,was,were,been
I am a student.
you are friend.
he is a doctor.
you will be late for school.
She was watching TV yesterday afternoon.
系动词有以下单词：be,is,are,am,was,were,been
I am a student.
you are friend.
he is a doctor.
you will be late for school.
She was watching TV yesterday afternoon.
