The correct answer is: C) to process uranium and use it to build and perfect atomic weapons.
The Manhattan Project was an United States government research project from 1942 to 1945. Its objective was to design and build an atomic bomb. It's essential fissionable component was Uranium-235, which needed to be suitable for use in an actual weapon. Several methods to achieve this were explored.
The reason of this project was the discovery of german physicists's knowledge of uranium. The U.S. thought germans would design nuclear weapons and use them against them.