there any possible way to help them get rid of such a bad habit--- Is there any possible way to help them get rid of such a bad habit?--- To tell the truth,it’s very hard.But we __________on this problem trying to improve the situation.A.worked B.had worked C.are working D.had been working应该选C.我知道是“我们一直在努力解决”的意思、但D 为什么不对?过去完成进行时表示”我们过去就一直在努力了“为嘛不对捏

there any possible way to help them get rid of such a bad habit
--- Is there any possible way to help them get rid of such a bad habit?
--- To tell the truth,it’s very hard.But we __________on this problem trying to improve the situation.
A.worked B.had worked C.are working D.had been working
应该选C.我知道是“我们一直在努力解决”的意思、但D 为什么不对?过去完成进行时表示”我们过去就一直在努力了“为嘛不对捏