Correct answer: A. 51
Explanation: The direct answer is A, 51. When the United Nations Charter came into force in 1945, the UN had 51 original member states. The figure refers to the founding members at that time, not the much larger membership the organisation has today. Step by step: the UN was created after the Second World War; its Charter became effective in 1945; 51 countries were counted as the original members. Option A is correct. Option B, 100, is too high for the original membership and confuses the founding number with a later total. Option C, 15, is not the number of original members; it may remind a student of the membership of the Security Council, but that is a different fact. Option D, 5, refers to the permanent members of the Security Council, not all founding members. Exam cue: 1945 and 51 belong together.