一个完整而正确的句子里只能有一个谓语，另一个或其他个动词就要变换形式成为非谓语动词。
I like playing football.
（like是谓语，playing是非谓语动词）
非谓语动词有三种形式：to do、doing 、done
to do表将来，表目的
I want to go fishing.
To get a great grade I try my best.
doing表进行表主动
I am reading books.
I saw a girl standing here.
done表完成，表被动
I have done my homework.
Enjoying music makes me feel relaxed.
