The correct answer is D. The Trusteeship Council.
The Trusteeship Council is one of the six principal organs of the United Nations. It was established in 1945 to oversee the administration of trust territories, which were territories that were not self-governing and were placed under the administration of a trusteeship agreement with the United Nations.
The Trusteeship Council has virtually accomplished its object as all 11 trust territories have achieved self-government or independence. The last trust territory, Palau, became independent in 1994.
The Security Council is responsible for maintaining international peace and security. It has 15 members, five of which are permanent members (China, France, Russia, the United Kingdom, and the United States) and 10 of which are elected by the General Assembly for two-year terms.
The General Assembly is the main deliberative organ of the United Nations. It has 193 members, each of which has one vote. The General Assembly meets in regular sessions every year and in special sessions when necessary.
The International Court of Justice is the principal judicial organ of the United Nations. It settles legal disputes between states and gives advisory opinions on legal questions referred to it by authorized international organs and specialized agencies.
The Trusteeship Council is the only principal organ of the United Nations that has virtually accomplished its object.