在和老师进行长时间的谈话后,我们终于找到了解决那个问题的办法。

After we had a long conversation with our teacher, we find a method to solve the hard queston at last.
B. After we had a long conversation with our teacher, we finally worked out a solution to the problem.
C. After a long talk with our teacher, we find a way to control the problem at last.
D. After we talked a long time with our teacher, we finally slove the hard problem.