四、阅读短文,回答问题
For Chinese students in middle school, there is an important exam that everyone wants to pass. It's the Senior High School Entrance Exam (中考). It's clear that they can't enter the high school if they fail the exam. So they are really under too much pressure (压力), especially (尤其) the students in Grade 9. They have to work harder than they did, and they usually have different school life from that in Grade 7.

One school in Changzhou surveyed 500 students in Grade 9 about how their life has changed since (自从) they were in Grade 9. There is no doubt (疑问) that they spend so much time on their schoolwork that they sleep less than they did in Grade 7. Most of the students sleep less than 8 hours because they have to stay up late to finish the homework and get up at 6:00 in the morning. One good thing is that students in Grade 9 exercise more. Because scores of PE in the Senior High School Entrance Exam are 40 points, the schools pay attention to the time of exercising. The survey also shows the students have no time to relax after school, such as watching TV, chatting on the phone and so on.
As for weekend activities, about 85% of the students take after-school classes, like English and Maths classes. They think it's more difficult to get better scores in these two subjects. For the PE test, they still keep exercising on weekends.
The parents are very happy to see their kids work harder for their dreams, but they all agree the kids are too tired every day.
前 4 题每题的答案不超过 10 个词,第 5 题的答案词数不限。
1. What does the underlined word "they" refer to (指的是)?______
2. Do students in Grade 9 sleep less than they did in Grade 7?______
3. Why do students in Grade 9 spend more time on exercise than they did in Grade 7?______
4. How many students take after-school classes in the survey according to Chart 2?______
5. What changes happened to you after you entered Grade 8?______