平面上向量OA绕点O逆时针方向旋转π2得向量OB，且2OA+OB=（7，9），则

阅读理解。

     I am an eighth-grade student at Central Middle School. In my three years at the school, I have played

soccer, basketball, and baseball. I love sports and really enjoy being part of a team. Playing on our school

sports teams has been the best part of middle school for me. I know I'm lucky that I've had this opportunity.

     Some kids have not been so lucky. In fact, many kids who love sports don't have the chance to play on

a school team. That's because, to make a team, you have to try out. The idea is that kids who are good at

sports will do well in tryouts and make the team. But what about the kids who don't do well during tryouts?

Maybe they are ill that clay, or nervous, or are just having a bad day, so they don't play their best. They don't

make the team, and that is too bad.

     Also, there are kids who really don't have the skills to play well. They never make a team, and that isn't

fair either. How will kids ever learn the skills if they don't have a chance to play? Remember, this is school

and students are here to learn. All kids should have the chance to learn sports skills and teamwork by playing

on a school sports team.

     There are other reasons why every student should have the chance to play sports. Sports are important

for good health and fitness. They help kids feel good about themselves and their school. They build friendships

among teammates. Coaches are good role models, and students who play team sports learn good sportsmanship. And, most important, team sports are fun! Players have fun playing, and their parents have fun watching and

cheering for the team. So, sports bring kids and parents together, too.

     By now you know how I feel. Every kid who wants to play on a school sports team should have the

chance. These teams are for fun and fitness-they're not professional teams! Let's change the rules for

making a team. Let's get rid of tryouts. Let's give every student at Central Middle School the chance to

wear a team uniform.

1. How many kinds of sports has the writer played in the three years at school?

A. Two

B. Three

C. Four

D. Five

2. The writer believes that tryouts are _______.

A. fun

B. hard

C. useful

D. unfair

3. Which of the following is NOT true according to the fourth paragraph?

A. Sports bring kids and parents together.

B. Sports build friendships among teammates.

C. Sports help kids feel good about themselves.

D. Sports are fun and make students study better.

4. The writer's main purpose for writing this article is to _______.

A. advise kids not to try out for a school team

B. tell about exciting moments on sports fields

C. make people believe all kids should play team sports

D. share his opinions of playing team sports with readers

设f （x）=4^x-2^x+1，则f^-1（0）=______．

影响汽车行驶的空气阻力因素有哪些？

严守纪律和遵守规章制度必须始终注重（）。