问题
选择题
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
答案:D
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。