单选题 There are many ways to keep healthy. It comes up to three points. First, eat good meals. Eating more vegetables and colorful food will make you feel good. Don't eat too much fat or processed food such as bacon, dried fruit and sausage. Second, enough sleep is very important. Go to bed before 23:00 and sleep eight hours a day. If you go to bed late, you may have a headache the next day. At last, it's necessary to take exercise. Exercise can help you build strong body and keep relaxed小题:How long should you sleep