题目内容

Although the causes of cancer ________, we do not yet have any practical way to prevent it．
A．have uncoveredB．have been uncovering
C．are uncoveringD．are being uncovered
D
考查时态语态，句意是;虽然癌症的原因正在被揭示出来，我们还是没有实用的方法来阻止它，因为癌症是被揭示，用被动式，几个选项只有A是现在进行时的被动。选D。
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