Nowadays, lots of students in Shenzhen complain that they have too much homework. Because of this, they feel unhappy about learning at school. According to a survey, a pupil has to spend two hours finishing the homework every day. It usually takes three hours for a middle school student and four hours for a high school student to finish the homework every day. Students in Grade Nine often do their homework until midnight. And all of them have to get up at as early as six o'clock the next morning. Mr. Li, a doctor in a hospital, told me yesterday, "Half of the students in Shenzhen are sub-healthy . The lack   of sleep makes them tired and their health is becoming poorer and poorer." Many parents worry about _ . What does the passage mainly tell us?
Many children are seriously ill. Children in Shenzhen study well. Too much homework keeps the students in poor health. How long students spend on their homework