It seems to happen with depressing frequency—sunny skies turn to rain just as the weekend arrives. Now Spanish researchers say t

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问题     It seems to happen with depressing frequency—sunny skies turn to rain just as the weekend arrives. Now Spanish researchers say they have evidence that in some parts of Europe the weather really does follow a weekly cycle, although not in the straightforward way that the anecdote might suggest.
    Evidence has been mounting over the years that the weather in certain partsof the world, including the US, Japan and China, can be driven by the weekly cycle of human activity. This is because we tend to produce more air pollution during the week and less at the weekend. Evidence that such an effect occurs in Europe is controversial and has been harder to come by. Arturo Sanchez-Lorenzo of the University of Barcelona, Spain, and his colleagues examined data gathered between 1961 and 2004 from weather stations across Spain to see whether such a pattern existed. They claim to have found it in Spain, as well as hints of weekly changes in air circulation more broadly over Western Europe.
    The result is puzzling, but it is known that airborne pollutants produced by human activity can affect the weather in a variety of ways. For example, particles can be heated by absorbing sunlight, which in turn heats the air and changes air circulation patterns. Pollutant particles can also provide seeds for cloud formation. Exactly which effect has the greatest influence seems to depend on conditions that vary season by season. They also found signs that air pressure in Western Europe tends to be lower midweek than at the weekend in data from a global database. This suggests that the human influence on weather goes beyond known local effects, says team member Josep Calbo of the University of Girona in Spain.
    However, it is not clear whether the team’s findings are statistically significant, says Thomas Bell of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was part of a team that found a stronger weekly cycle in the US. "This whole enterprise of looking for weekly cycles is rife with possibilities for misleading oneself."
    Why a weekly cycle would be less noticeable in Europe than in the US and Asia is still unknown. No weekly cycle has ever been found in the UK, probably because the weather is dominated by large systems blowing in from the Atlantic Ocean. These larger systems may be harder for weekly pollution cycles to influence, points out Douglas Maraun of the University of East Anglia in Norwich, who studies UK precipitation. "I doubt that there is a weekly influence of human activity on such a large weather system," he says.
The reason why weather changes are possibly due to human factors is that _____.

选项 A、the weather usually follows a weekly cycle
B、when people stay at home, they are careful with pollutants production
C、air circulation acts in different manners because of deliberate human interference
D、different activities on weekdays and weekends have imposed effect on the air

答案D

解析 事实细节题,考查因果细节。该段第一句提到天气受人类活动周循环的影响,第二句的because表明原因:我们在工作日造成的空气污染往往要多些,周末则少些。可见,正是由于人们在工作日和周末的不同活动给大气造成了影响,虽然这种影响在欧洲争议较大且证据不足,但第二段第五句说明这种现象存在,故与题干中的possibly相符,选D项。
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