在详细地研究这个问题后，我们终于找到了解决它的方法。
A、 Studying it carefully, we finally found out a solution to the problem.
B、 Having studied it carefully, we finally found out a solution to the problem.
C、 After studied it carefully, we finally found out a solution to the problem.
D、 Have been studied it carefully, we finally found out a solution to the problem.