Air pollution triggers more heart attacks than using cocaine and poses as high a risk of sparking a heart attack as alcohol, cof

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问题     Air pollution triggers more heart attacks than using cocaine and poses as high a risk of sparking a heart attack as alcohol, coffee and physical exertion, scientists said on Thursday. Anger, marijuana(大麻)use and chest or respiratory(与呼吸有关的)infections can also trigger heart attacks to different extents, the researchers said, but air pollution, particularly in heavy traffic, is the major culprit(问题的起因).
    The findings, published in The Lancet journal, suggest population-wide factors like polluted air should be taken more seriously when looking at heart risks, and should be put into context beside higher but relatively rarer risks like drug use. Tim Nawrot of Hasselt University in Belgium, who led the study, said he hoped his findings would also encourage doctors to think more often about population level risks. "Physicians are always looking at individual patients—and low risk factors might not look important at an individual level, but if they are prevalent in the population then they have a greater public health relevance," he said in a telephone interview.
    Nawrot’s team combined data from 36 separate studies and calculated the relative risk posed by a series of heart attack triggers and their population-attributable fraction(PAF)—in other words the proportion of total heart attacks estimated to have been caused by each trigger. "Of the triggers for heart attack studied, cocaine is the most likely to trigger an event in an individual, but traffic has the greatest population effect as more people are exposed to(it)," the researchers wrote. "PAFs give a measure of how much disease would be avoided if the risk was no longer present."
    A report published late last year found that air pollution in many major cities in Asia exceeds the WHO’s air quality guidelines and that toxic cocktails of pollutants results in more than 530 000 premature deaths a year. While passive smoking was not included in this study, Nawrot said the effects of second-hand smoke were likely to be similar to that of outdoor air pollution, and noted previous research found that bans on smoking in public places have significantly reduced heart attack rates.
    Tim Chico, a heart specialist at the University of Sheffield who was not involved in this research, said it would help health authorities focus on the most important triggers. "However, what triggers the heart attack should be considered the ’ last straw.’ The foundations of heart disease that lead to a heart attack are laid down over many years," he said in an e-mailed comment. "If someone wants to avoid a heart attack they should focus on not smoking, exercising, eating a healthy diet and maintaining their ideal weight. "
What does Tim Chico mean by saying "last straw"(Line 3, Para. 5)?

选项 A、However small it is, we should pay attention to every heart attack risk.
B、Though exposed to traffic every day, we can still protect ourselves.
C、We need to focus on the most important heart attack trigger.
D、If we develop a healthy lifestyle, we can conquer heart attack.

答案A

解析 语义理解题。由定位句可知,Tim Chico表示任何引起心脏病的因素都应该被视为“最后一根稻草”,从心脏病的形成到发作是长年累积的结果。可见他用“最后一根稻草”表明每一种致病风险都应该被重视,不论它多么微不足道,都有可能对心脏病人构成“致命一击”,因此答案为A)。
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