做作业,遇到问题了,英语……
问题描述：
做作业,遇到问题了,英语……
Although the causes of cancer ___,we do not get have any practical way to prevent il.
A.are being uncovered B. have been uncovering
C.are uncovering D.have uncovered
答案先不说,会的帮帮忙啊,作业啊~~急·
尽量详细点，谢谢~~~
答
应该选A,这时是表状态,所以应该选择A,D是表达完成时的,不对