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  3. Community cancer clusters are viewed quite differently by citizen activists than by epidemiologists. Environmentalists and conce

Community cancer clusters are viewed quite differently by citizen activists than by epidemiologists. Environmentalists and conce

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问题     Community cancer clusters are viewed quite differently by citizen activists than by epidemiologists. Environmentalists and concerned local residents, for instance, might immediately suspect environmental radiation as the culprit when a high incidence of cancer cases occurs near a nuclear facility. Epidemiologists, in contrast, would be more likely to say that the incidences were "inconclusive" or the result of pure chance. And when a breast cancer survivor, Lorraine Pace, mapped 20 breast cancer cases occurring in her West Islip, Long Island, community,  her rudimentary research efforts were guided more by hope--that a specific environmental agent could be correlated with the cancers than by scientific method.
    When epidemiologists study clusters of cancer cases and other noncontagious conditions such as birth defects or miscarriage, they take several variables into account, such as background rate (the number of people affected in the general population), cluster size, and specificity (any notable characteristics of the individual affected in each case). If a cluster is both large and specific, it is easier for epidemiologists to assign blame. Not only must each variable he considered on its own, but it must also be combined with others. Lung cancer is very common in the general population. Yet when a huge number of cases turned up among World War Ⅱ shipbuilders who had all worked with asbestos, the size of the duster and the fact that the men had had similar occupational asbestos exposures enabled epidemiologists to assign blame to the fibrous mineral.
    Although several known carcinogens have been discovered through these kinds of occupational or medical clusters, only one community cancer cluster has ever been traced to an environmental cause. Health officials often discount a community’s suspicion of a common environmental cause because citizens tend to include cases that were diagnosed before the afflicted individuals moved into the neighborhood. Add to this the problem of cancer’s latency. Unlike an infectious disease such as cholera, which is caused by a recent exposure to food or water contaminated with the cholera bacterium, cancer may have its roots in an exposure that occurred 10 to 20 years earlier.
    Do all these caveats mean that the hard work of Lorraine Pace and other community activists is for nothing? Not necessarily. Together with many other reports of breast cancer clusters on Long Island, the West Islip situation highlighted by Pace has helped epidemiologists lay the groundwork for a well designed scientific study.  
Activists may mistakenly consider a particular incidence of cancer as part of a com- munity cluster despite the fact that ______.
选项 A、the affected individual never worked with any carcinogenic material
B、the cancer was actually caused by a long-ago exposure
C、the size of the cluster is too small to be meaningful
D、the cancer actually arose in a different geographic location
答案D
解析 第一段提到，当一个社区出现患癌症的群体时，公民中的社会活动家与流行病学家的看法经常产生分歧，例如，当住在核设施附近的病人痛症患病率很高时，环境保护主义者和相关的当地居民(根据上句当属于citizen activist的范围)立刻会怀疑到环境内的辐射源是导致癌症的主要原因。而传染病学家则会说证据还不确凿，或者说这种情况纯粹是巧合。
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