英语高考28.Although the causes of cancer ____,we do not yet have any practical way to prevent it.

题目

英语高考28.Although the causes of cancer ____,we do not yet have any practical way to prevent it.
28.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
如果选项E是have been uncovered,那是选E还是A?,还是EA都行?
如何知道语义是正在被发现还是已经被发现?
要详解.

答案

虽然导致癌症的原因已经被发现了,我们却还没有可行的方法预防它.
a. 正在被发现