假设你是刘勇，你的朋友露西（Lucy）向你询问如何保持健康。请你给她发封电子邮件提些建议。内容要点如下：
（1）注意合理饮食。多吃鱼、蛋和豆类等，特别是新鲜蔬菜和水果，不要吃太多甜食。
（2）坚持锻炼身体。劳逸结合，多参加体育活动。
（3）保证充足的睡眠。不要熬夜，每天至少睡8个小时。

【考点】应用文；环境保护．

【答案】Dear Lucy，
   How nice to hear from you!In your letter you asked me how to keep healthy.I would like to give you some advice.
   As you know，we teenagers grow very fast，so we need plenty of nutritious foods，such as fish，meat，and beans，especially fresh vegetables and fruits.You'd better not eat too much food rich in sugar or fat.Besides，you should take physical exercise regularly instead of studying in the classroom all the time.For example，you can play basketball with your friends or swim after school.What's more，having enough sleep is very important.So I advise that you should have at least eight hours of sleep every day and not stay up too late in the evening.Only in this way can you keep fit.
Yours，
Liu Yong