动词不定式作状语，用来修饰动词、形容词、副词或整个句子。通常表示目的、原因、结果、程度等。
1.用在一些形容词或动词后面作原因状语。
He is sad to hear the bad news.
他听到坏消息很伤心。
She thrilled to get the key.
他拿到钥匙很激动。
2.动词不定式可在句中作目的状语。
不定式作目的状语，既可放在句首，也可以放在句尾。
为了加强语气，也可用so as to do 或 in order to do结构作目的状语。
in order to放在句首句尾都可以，so as to 只能放在句尾。
He studies hard to get good grades.
他努力学习是为了取得好成绩。
They work hard in order to/so as to make a better life.
为了创造更好的生活，他们努力工作。
In order to make a better life,they work hard.
3.动词不定式作结果状语。
a."too+adj./adv.+to do"
太…而不能
The work is too hard for me to finish.
完成那个工作对我来说太难了。
He speaks too fast for me to follow.
他讲得太快，我跟不上。
b."(only/all+too+adj./adv.+to do)"
非常
I am only too happy to help you.
能帮助你我非常开心。
They are all to helpful to do this.
他们都很乐于做这件事。
c."adj./adv.+enough+to do"
足够…
She is not old enough to go to school.
她还不够大，不能去上学。
The father walked slowly enough to make his child follow him.
为了让他的孩子跟上他，这位父亲走得很慢。
d."only(just) to do"表示令人失望的、不愉快的结果。
He studied hard only to find he had failed the exam.
他努力学习，结果却发现考试失败了。
The teacher spoke so slow as to make his students understand him.
为了让学生们听懂，这个老师讲的很慢。
He is such a fool as to do the silly things.
他就是个傻瓜，才做这样愚蠢的事。