7.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
网友回答
(答案→)A. are being uncovered
B. have been uncovering
C. are uncovering
D. have uncovered
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。