Question

--Why are the windows so dirty?
--Because we_________them for a long time.
A. have cleaned          B. haven't cleaned       C. didn't clean

Answer 1

B

句意：窗户为什么这么脏？——因为我们有很久不打扫他们了。结合语境可知下文描述的是从过去一直持续到现在的动作，否定语气，故用现在完成时态否定形式，选B。