阅读下面的短文，根据短文内容回答问题。
New rules and behaviour standards (行为规范) for middle school students came out (颁布) in March.
Middle schools are going to use a new way to decide who the top students are. The best students won't
only have high marks. The following are some of the new rules.
Tell the truth. Have you ever cheated (作弊) in an exam? Don't do it again! That's not something honest
students should do.
Do more at school. Good students love animals and care for other people. April is Bird loving Month in
China. Is your school doing anything to celebrate it? You should join! In that way, you can learn more about
animals and how to protect (保护) them.
Be open to new ideas. Have you ever thought people could live on the moon? Maybe you'll find another
earth in space in the future. Everyone's new ideas are important.
Protect yourself. Has a thief ever taken money from one of your classmates? Don't let it happen to you.
If you have to go back home late, you should let your parents know.
Use the Internet carefully. The Internet can be very useful for your study. But some things on the Internet
aren't for kids, so try to look at the good web pages (网页). You can use the web pages for fun or homework.
1. What should the best students do in an exam?
2. What should you do if you have to go back home late?
3. What can the children use the good web pages for?
4. When did the new rules come out?
5. Which new idea do you think may come true?
得，离地越高的太空垃圾运行速率越大
，垃圾的运行周期：
，所以r越小，即离地越低的太空垃圾运行周期越小，故A正确；由牛顿第二定律可得：
，垃圾运行的角速度
，所以轨道半径越大，即离地越高的垃圾的角速度越小，故B正确；由牛顿第二定律可得：
，垃圾运行的线速度
，轨道半径越大，即离地越高的垃圾线速度越小，故C错误；由线速度公式