问题 选择题
如图所示的LC振荡电路,在某时刻的磁场方向如图所示,则下列判断不正确的是(   )

A.若磁场正在增强,则电场能正在减少,电容器上极板带正电

B.若磁场正在减弱,则电场能正在增强,电容器上极板带正电

C.振荡电流的变化周期为:

D.电场能量的变化周期为:π

答案

答案:A

阅读理解

阅读理解。

     Sports can help you keep fit and get in touch with nature. However, whether you are on the mountains,

in the waves, or on the grassland, you should make it clear that your choice of sports might have great

influence on the environment.

     Some sports are resource-hungry. Golf, as you may know, eats up not only large areas of countryside,

but also tons of water. Besides, all kinds of chemicals and a great deal of energy are used to keep its fields

in good condition. This causes environmental problems. For example, in the dry areas of Portugal and Spain,

golf is often the cause of serious water shortage in some places.

     There are many environment-friendly sports. Power walking is one of them that you could take up today.

You don't need any special equipment except a good pair of shoes; and your don't have to worry about

resources (资源) and you purse. Simple and free, power walking can also keep you fit. If you walk very

often, it will be good for your heart and bones. Experts (专家) say that 20 minutes of power walking daily

can make you feel less nervous, sleep well and have better weight control.   

     Whatever sport you take up,you can make it greener by using environment-friendly equipment and buying

products made from recycled materials (再生材料). But the final purpose should be "green gyms". Compared

with traditional health clubs and modern sports centers, they are better choices. Members of green gyms play

sports outdoors, in the countryside or other open spaces. There is no special requirement for you to start your

membership. And best of all, it's free.

1. Which of the following sports is environment-friendly?

A. Swimming in a health club.

B. Playing football on the sports field.

C. Bicycle-riding in the countryside.

D. Playing volleyball in a sports center.

2. Which statement about power walking is TRUE?

A. It needs special shoes.

B. It's very simple but costs a lot.

C. It makes you worry about resources.

D. It's good for health and the environment.

3. The writer writes the passage in order to _____.

A. show us how different sports help us

B. encourage us to take up green sports

C. introduce some environment-friendly sports

D. tell us how sports influence the environment

单项选择题