The correct answer is A) he refused to promise to allow free elections in Eastern Europe.
What Stalin do at the meeting in Postdam that alarmed President Truman was that he refused to promise to allow free elections in Eastern Europe.
The Postdam Conference (July 17-August 2, 1945) was a meeting of Allied Forces held in Postdam, Berlin, Germany. The participants were President Harry Truman from the United States, Prime Minister Winston Churchill of the Great Britain, and Soviet Premier Joseph Stalin of the Soviet Union. The world leaders disussed the peace terms after World War II but no treaties were signed. During the Conference, what Stalin do at the meeting in Postdam that alarmed President Truman was that he refused to promise to allow free elections in Eastern Europe.