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

答案及解析： A

解析：

分析语境逻辑不难发现，该空表示“现在正在被揭示”，应填现在进行时被动语态动词形式are being uncovered。