Although the causes of cancer ___,we do not yet have any practical way to prevent it.are being uncovered/ have been uncovering选哪个答案对呢,为什么?答案是are being uncovered 为什么呢?

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Althoughthecausesofcancer___,wedonotyethaveanypracticalwaytopreventit.arebeinguncovered/havebeenunco

Although the causes of cancer ___,we do not yet have any practical way to prevent it.are being uncovered/ have been uncovering选哪个答案对呢,为什么?答案是are being uncovered 为什么呢?
Although the causes of cancer ___,we do not yet have any practical way to prevent it.
are being uncovered/ have been uncovering
选哪个答案对呢,为什么?
答案是are being uncovered 为什么呢?

Although the causes of cancer ___,we do not yet have any practical way to prevent it.are being uncovered/ have been uncovering选哪个答案对呢,为什么?答案是are being uncovered 为什么呢?
这个题目应该是are being uncovered
原因如下:
这个句子是被动语态,the causes 作为被研究的对象,只能被研究,
如果用have been uncovering 暗示着句子的主语是人了.与前面相矛盾了 :)

have been uncovering!