The restructuring agency
explored several alternatives, including complete and partial liquidation of assets, but has not found any feasible solution to the problems faced by the company.
(A) explored several alternatives, including complete and partial liquidation of assets, but has not found -> Something explored (past tense) and has not found (present tense), It doesn't make sense. They must be exploring till now. Incorrect.
(B) had explored several alternatives, which include complete and partial liquidation of assets, but has not found -> had explored- we don't see two actions. Incorrect.
(C) explored several alternatives, including complete and partial liquidation of assets, but did not found -> Explored and found both are in past, it doesn't make sense. Intended meaning is solution is yet to be found. Incorrect.
(D) has explored several alternatives, including complete and partial liquidation of assets, but has not found -> It is better. Explored (from past to present) and found (from past to present). Let's keep it.
(E) has explored several alternatives, including complete and partial liquidation of assets, but did not find ->"has Explored" is in present and "did find" is in past, it doesn't make sense. Incorrect.
So, I think D.