Although the causes of cancer we do not yet have any practical way to prevent itA. have

问题补充：

Although the causes of cancer , we do not yet have any practical way to prevent it．

A. have uncovered

B. have been uncovering

C. are uncovering

D. are being uncovered

答案：

A. have uncovered

B. have been uncovering

C. are uncovering

(答案→)D. are being uncovered

解析：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。