根据短文内容，选择正确答案。 If you often feel tired and the doctor can't find anything wrong with you, you may be in a state of subhealth(亚健康). Subhealth is a state between health and illness. Most of the subhealthy people are middle-aged ones who are usually stressed out because of work and family. And some of them are students who are having exams.If you are subhealthy, it is not difficult for you to become well soon. You should have good living habits. For example, you should get up early and go to bed early. And you should exercise regularly. Exercising can keep you healthy. As for meals. it is better to eat less salt and sugar. Vegetables, fruit and fish are important to your body. You should eat more of them. It is not good to eat too much at one meal, because it may cause unhealthy changes in the digestive tract(消化道). And at last, a balanced diet is very helpful in staying away from subhealth.（1）How may you feel if you're subhealthy?A．Happy.B．Comfortable.C．Tired.D．Sad.（2）According to the passage，who will probably be subhealthy?A．Teachers and students.B．Parents and children.C．Middle-aged people and students.D．The young and the old.（3）What should you do if you are subhealthy?A．Relax and have good living habits.B．Go to see the doctor and ask for some medicine.C．Go to hospital in foreign countries.D．Stay at home and not talk to others.（4）What is the main idea of the passage?A．What is subhealth?B．How to keep away from subhealth.C．How to keep subhealthy.D．Why are you subhealthy?