题目内容：

    Youth is a stressful time from friends to school to families, and stressful situations become common. The body can respond (反应) with faster breathing, a fast beating heart, tense (绷紧的) muscles and drop of sweat. And teens who breathe polluted air appear to respond most strongly to stress, a new study shows.

Jonas Miller, a psychologist working at Stanford University ,studied whether or how air pollution might affect the body’s response to stress. Miller's team invited 144 teens to participate in a stressful test. Most of the kids lived in or near San Francisco,which has the worst air quality.

Before the test, the researchers used sensors(感测器) to record heart rates and sweat levels for five minutes as the kids rested. Then as the test began, a researcher read aloud the beginning of a story and the kids had five minutes to make up an exciting ending to the story. They would have to memorize their ending and present it aloud to a judge. After finishing this task, the kids were asked to do math problems, which obviously was a harder task. If he or she made a mistake, the judge let the student start over. The whole time, sensors recorded heart rates and sweat levels.

Miller found all the students had similar heart rates and sweat levels at rest. But as the test got difficult, differences began to appear. Kids from places with more air pollution responded more strongly to stress and their heartbeats became irregular. They sweated more than teens who lived in cleaner places.

"The teens' bodies were preparing to deal with possible challenges in the environment and such bodily responses to stress were linked to negative feelings", Miller concludes. Over time, he says, "these responses can contribute to both physical and mental health problems."

This study has proved the negative heath effects of air pollution among teenagers. Therefore, teenagers should try to avoid their exposure (暴露) to air pollution They should consider limiting their time outside during rush hour, especially on days when air pollution is particularly strong.

1.What happened to teens in stressful situations?

A.Their bodies react strongly.

B.Their muscles cause pain.

C.They become seriously sick.

D.They have trouble in breathing.

2.What can we learn about the test?

A.The judge of the test was strict with the kids.

B.The kids enjoyed making up endings of stories.

C.Those breathing polluted air doesn't have more stress in life.

D.The kids gradually felt more stress in the process.

3.From the study we can infer that tens should ____.

A.solve their mental heath problems

B.spend less time outside in heavy traffic

C.learn to deal with stressful situations

D.enjoy more outside activities in good weather

4.Where is the passage probably from?

A.A report on pollution. B.A geography book.

C.A psychologist's diary. D.A science magazine.