Answer:
B. the Soviet Union
What was the intended purpose of the Potsdam Conference?
The major purpose of the Potsdam summit between Truman, Stalin, and Churchill—later replaced by Atlee—was to determine Germany's postwar position. How might a nation that has been split into four zones of occupation be united? What would the borders of Germany be after the war? (Stalin insisted and was granted the port of Konisberg, which is now Kaliningrad.) Would Germany be allowed to remilitarize, under allied supervision and control ? Would Germany be allowed to reindustrialize, or would it become mostly an agricultural country? (A plan that Stalin and FDR's Treasury Secretary Henry Morgenthau both supported.) Would elections be held to bring about German reunification? What would the process be for de-Nazification? How would the atrocities caused by the German invasion and occupation be made up to the USSR? Some historians attribute the start of the Cold War to this conference rather than Churchill's "Iron Curtain" speech one year later because none of these concerns were resolved at Potsdam.
Though it wasn't discussed in any detail, ending the war with Japan was another subject. Stalin vowed to launch a comprehensive offensive against the Japanese in Manchuria, and he did so. In his memoirs, Churchill writes that when Truman informed Stalin that the United States had "a weapon of tremendous destructive powers" that would soon be used in the Pacific theater to finish the war, Stalin did not react in horror but instead grinned subtly. (Perhaps he was aware of the A-bomb already?)
Frustrated, Truman returned home. Churchill had, in the words of the British voters, "retired from high office" in favor of the Labour Party and Atlee, and Stalin was undoubtedly happy that he kept East Germany, which he then went on to loot.
Thank you,
Eddie