Which of the following is not a chief organ of the United Nations?

Article 7 of the UN Charter establishes six principal organs: the General Assembly, the Security Council, the Economic and Social Council, the Trusteeship Council, the International Court of Justice and the Secretariat. The "International Labour Organisation" is not among them; it is a specialised agency linked to the UN by agreement, whereas the Security Council, the ICJ and the General Assembly are principal organs.