Dear Jenny,
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 sweet.Also,you should take physical exercise regularly instead of studying in the classroom all the time.For example,you can play basketball or swim after school.What’s more,having enough sleep is very important.So I advise you to have at least eight hours of sleep every day and not to stay up too late.Only in this way can you keep fit.