问题
选择题
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
答案
答案：A
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。