__________ of the students are girls, and the rest _____ boys.

[　　]

A. Two third…is

B. The two third…are

C. Two thirds…are

D. Two thirds…is

Physical fitness is the result of many factors: good medical and gentle care, proper nutrition, enough rest and relaxation, and sensible personal habits. But these are never enough. An essential factor is regular physical activity for a body to function well.

All of us know that ordinary movements like running, jumping, and bending are made possible by muscles. Muscles also do many other things. They suck air into your lungs, push food along your digestive tract（消化管）, and tighten your blood vessels to raise blood pressure when you need more pressure for an emergency. Your heart is a muscular pump（强健的泵或抽水机）.

When your muscles are not used, or not used enough, they do not develop and grow properly. They soon become weak, smaller in size and lose their ability to do the jobs they were meant to do.

Recent studies showed that the average high school student spend fifteen to thirty hours a week watching television and only two hours a week in organized play or exercise. That is one reason why one-third of the 200,000 pupils tested for the President's Council on Physical Fitness failed a simple test of strength. Some of the boys and girls could not raise themselves to a sitting position without using their hands!

Cars and buses, lifts, TV and push-button machines all tend to reduce physical activity. But our bodies still need exercise. Without it they soon become weak and unattractive.

1． In the article，muscles are said to do all of the following except _______ .

A．suck air 　B. run， jump and bend 　C. tighten blood vessels 　D. reduce pain

2． The thing to keep physical fitness discussed in this article is _______ .

A．strength B. nutrition C. skill D. exercise

3．The author advises us to _______ .

A．replace physical activity with watching TV

B. fail 200,000 students on a physical fitness test

C．exercise our bodies regularly

D. do annual medical checkups

4．According to the article, high school students _______.

A. are mostly weak

B. often suffer from lung troubles

C. lack enough exercise

D. should watch less TV programs