Although the causes of cancer ___,we do not yet have any pra

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?

胡萝卜0916 1年前已收到2个回答举报

答案在风中飘呀飘幼苗

共回答了15个问题采纳率：93.3% 举报

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 :)

1年前

zhangshiju123 幼苗

共回答了82个问题举报

have been uncovering!

1年前

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