To What Extent Was Harry Truman Involved with the Manhattan

To what extent was Harry Truman involved with the Manhattan Project at the time that he assumed the presidency upon Franklin Roosevelt's death on April 12, 1945?

A) Truman was completely unaware of the Manhattan Project until he was informed about it upon Roosevelt's death.
B) Truman was not made aware of the Manhattan Project until the first test bomb was exploded while he was at the Potsdam Conference several months after assuming the presidency.
C) Roosevelt immediately made Truman aware of the Manhattan Project after they were declared the victors of the 1944 presidential election.
D) As a former U.S. senator, Truman had been extensively involved with the Manhattan Project since Roosevelt first authorized it after U.S. entry in World War II in late 1941.