The correct answer is B, the United Nations.
The idea of the UN was elaborated in the declaration issued at the Yalta Conference held by the allies in February 1945. There, Roosevelt suggested the name of the United Nations.
On April 25, 1945 the Conference of San Francisco was held. In addition to the governments, non-governmental organizations were invited. On June 26, the fifty nations represented at the conference signed the Charter of the United Nations. Poland, which had not been represented at the conference, added its name later among the founding signatories, for a total of 51 States.
The UN began its existence after the ratification of the Charter by the Republic of China, France, the Soviet Union, the United Kingdom and the United States and the vast majority of the other 46 members. The first session of the General Assembly was held on January 10, 1946.