leave no stone unturned.

Options

A. search for the hidden treasure
B. do a futile task
C. be known for achieving a tremendous feat
D. try every possible course of action in order to achieve something

Answer

D

Explanation

leave no stone unturned to do everything you can to achieve a good result. Look at the sentence: He left no stone unturned in his search for his natural mother. The best option is try every possible course of action in order to achieve something.