British cancer researchers have found that childhood leukaemia is caused by an infection and clusters of cases around industrial

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问题      British cancer researchers have found that childhood leukaemia is caused by an infection and clusters of cases around industrial sites are the result of population mixing that increases exposure. The research published in the British Journal of Cancer backs up a 1988 theory that some as yet unidentified infection caused leukaemia--not the environmental factors widely blamed for the disease.
     "Childhood leukaemia appears to be an unusual result of a common infection," said Sir Richard Doll, an internationally-known cancer expert who first linked tobacco with lung cancer in 1950. "A virus is the most likely explanation. You would get an increased risk of it if you suddenly put a lot of people from large towns in a rural area, where you might have people who had not been exposed to the infection." Doll was commenting on the new findings by researchers at Newcastle University, which focused on a cluster of leukaemia cases around the Sellafield nuclear reprocessing plant in Cumbria in northern England. Scientists have been trying to establish why there was more leukaemia in children around the Sellafield area, but have failed to establish a link with radiation or pollution. The Newcastle University research by Heather Dickinson and Louise Parker showed the cluster of cases could have been predicted because of the amount of population mixing going on in the area, as large numbers of construction workers and nuclear staff moved into a rural setting. "Our study shows that population mixing can account for the (Sellafield) leukaemia cluster and that all children, whether their parents are incomers or locals, are at a higher risk if they are born in an area of high population mixing," Dickinson said in a statement issued by the Cancer Research Campaign, which publishes the British Journal of Cancer.
     Their paper adds crucial weight to the 1988 theory put forward by Leo Kinlen, a cancer epidemiologist at Oxford University, who said that exposure to a common unidentified infection through population mixing resulted in the disease.
According to the passage, which of the following is true?

选项 A、Most people believe childhood leukaemia is due to environmental factors.
B、Population mixing best explains the cause of childhood leukaemia.
C、Radiation has nothing to do with childhood leukaemia.
D、Children born in a large town are at higher risk of leukaemia.

答案A

解析 第一段最后一句话证明是正确的,B不对,因为人口混居是造成这种病多发的原因,而非致病的原因;C不对,因为尽管文中说没有确定这种病和辐射的关系,但并不表示它和辐射没有关系;D不对,因为这种病的高发区是人口混居区而非大城镇。所以正确答案应当为A。
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