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

问题补充：

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

A. are being uncovered

B. have been uncovering

C. are uncovering

D. have uncovered

答案：

(答案→)A. are being uncovered

B. have been uncovering

C. are uncovering

D. have uncovered

解析：考查时态。句意：尽管癌症的原因正在在揭开，我们仍然还是没有任何实用的方法来预防癌症。根据句意说明癌症的原因正在被揭开，使用的是现在进行时的被动语态。故A正确。