3.D. 利用问题句中的特征词(Nicholas A. Christakis)作为答案线索， 同时利用备选项B中的典型细节信息结构(eating habits)作为答案线索， 在文章中查找答案相关句：
Obesity can spread from person to person, much like a virus, researchers are reporting today. When one person gains weight, close friends tend to gain weight, too.
Their study, published in The New England Journal of Medicine, involved a detailed analysis of a large social network of 12,067 people who had been closely followed for 32 years, from 1971 to 2003.
The investigators knew who was friends with whom as well as who was a spouse or sibling or neighbor, and they knew how much each person weighed at various times over three decades. That let them reconstruct what happened over the years as individuals became obese. Did their friends also become obese? Did family members? Or neighbors?
The answer, the researchers report, was that people were most likely to become obese when a friend became obese. That increased a persons chances or becoming obese by 57 percent. There was no effect when a neighbor gained or lost weight，however, and family members had less influence than friends.
(第2题答案相关句)(第5段)It did not even matter if the friend was hundreds of miles away, the influence remained. And the greatest influence of all was between close mutual friends. There, if one became obese, the other had a 171 percent increased chance of becoming obese, too.
(第6段)The same effect seemed to occur for weight loss, the investigators say. But since most people were gaining, not losing, over the 32 years, the result was, on average, that people grew fatter.
(第7段)Dr. Nicholas A. Christakis, a physician(医生) and(兼) professor (教授)of medical(医学的) sociology(社会学) at Harvard Medical School(哈佛医学院)and a principal(主要的， 校长， 负责人) investigator(调查人) in the new study(研究), said one explanation (问题句中的核心词)was that friends affected(影响) each others(彼此)’ perception(理解)(perception是feeling的近义词) of fatness(肥胖). When a close friend (亲密的朋友)becomes obese, obesity may not look so bad.
答案相关句(第七段第一句)涉及到了Dr. Nicholas A. Christakia对于这种现象的解释：朋友之间对于肥胖的感知是互相影响的。因此D是答案。
4. Which factor(因素)of becoming obese (变得肥胖)is not mentioned (没有被提到)in this report(报告)?
A. social(社会的， 社交的) contact(接触，联系)
B. genetic information(遗传信息)
C. life style (生活方式)
D. environmental(环境的) influence
4.C. 利用备选项中的细节信息结构(A：social contact; B: genetic information; C: life style; D: environmental influence)共同作为答案线索，在文章中查找答案相关句：
Obesity can spread from person to person, much like a virus, researchers are reporting today. When one person gains weight, close friends tend to gain weight, too.
Their study, published in The New England Journal of Medicine, involved a detailed analysis of a large social network of 12,067 people who had been closely followed for 32 years, from 1971 to 2003.
The investigators knew who was friends with whom as well as who was a spouse or sibling or neighbor, and they knew how much each person weighed at various times over three decades. That let them reconstruct what happened over the years as individuals became obese. Did their friends also become obese? Did family members? Or neighbors?
The answer, the researchers report, was that people were most likely to become obese when a friend became obese. That increased a persons chances or becoming obese by 57 percent. There was no effect when a neighbor gained or lost weight，however, and family members had less influence than friends.
It did not even matter if the friend was hundreds of miles away, the influence remained. And the greatest influence of all was between close mutual friends. There, if one became obese, the other had a 171 percent increased chance of becoming obese, too.
The same effect seemed to occur for weight loss, the investigators say. But since most people were gaining, not losing, over the 32 years, the result was, on average, that people grew fatter.
(第7段/第3题答案相关句)Dr. Nicholas A. Christakis, a physician and professor of medical sociology at Harvard Medical School and a principal investigator in the new study, said one explanation was that friends affected each others’ perception of fatness. When a close friend becomes obese, obesity may not look so bad.
“You change your idea of what is an acceptable body type by looking at the people around you,” Dr. Christakis said.
The investigators say their findings can help explain why Americans have become fatter in recent years – each person who became obese was likely to drag along some friends!
Their analysis was unique, Dr. Christakis said, because it moved beyond a simple analysis of one person and his or her social contacts and instead examined an entire social network at once, looking at how a person's friend's friends, or influence on a person's weight or a spouse's sibling's friends, could have an influence on a person’s weight.
The effects, he said, “highlight the importance of contagion, that spreads through the network.”
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