Correct option is D
The Secretary-General is the chief administrative officer of the United Nations (UN) and heads the Secretariat, which is one of the six main organs of the UN.
The Secretariat: Handles the day-to-day work of the UN.Provides administrative support, conducts research, prepares reports, and implements decisions of other UN bodies.Headed by the Secretary-General, who is appointed by the General Assembly on the recommendation of the Security Council.
Additional Knowledge:
General Assembly – A deliberative body of all member nations.
Security Council – Responsible for international peace and security.
International Court of Justice – Judicial arm of the UN.