长方体和正方体的体积都可用底面积乘高来计算

阅读下面材料, 从A、B、C、D四个选项中选出最佳选项。

    Jumping rope(绳子)is a sport any student can learn to do．You can jump alone or with a friend．You can also help turn a long rope for many others to jump over．If you jump alone, you will need a short rope which should be just long enough for you．

    A rope should be turned slowly．It must also be turned high enough to let you jump safely．Turning the rope safely needs careful timing．In rope jumping, timing means turning the rope slowly enough so that you can jump over it at the right time without its hitting your feet．

  You will notice that when you jump rope, you breathe(呼吸)faster and your face has a healthy colour．But, if you jump too many times at first, you will get too tired．You must learn when to stop for rest(休息)before you jump again．As you practice, you can increase the number(次数)of times you jump without resting．

   American boys and girls like watching TV. Some children spend six hours a day at school and four to six hours a day in front of the TV sets. Some children even watch TV for eight hours or more on Saturday.
   Television（电视）is like books and films . A child can learn good things and bad things from it. Some TV programs help children to understand the news, the people and places from other countries. With TV, children do not have to go out to see films, they can hear interesting music or watch a game at home. But some programs are bad for children, so parents sometimes help them to find other interesting and useful things to do.