Which of the following is not a correct statement, given that all the listed bodies are agencies of the United Nations system?

Introduction / Context:
The United Nations system includes many specialised agencies and related organisations that work in specific areas such as finance, atomic energy and postal services. This question checks whether you know that several well known international institutions are formally associated with, or function as, agencies of the UN system. It uses a slightly tricky wording where "not an agency" is contrasted with an option stating that all listed organisations are in fact agencies.

Given Data / Assumptions:

• The bodies mentioned are the World Bank, the International Atomic Energy Agency (IAEA) and the Universal Postal Union (UPU).
• Option D says that none of the above statements is false, meaning all three are agencies in the UN system.
• We are asked which option is not correct, but the only way for that to be true is if all three organisations are indeed agencies, making the "None of the above" statement correct.

Concept / Approach:
The World Bank (in the broader sense, including IBRD and related institutions) is part of the World Bank Group, which functions as a specialised agency of the UN. The International Atomic Energy Agency (IAEA) is an independent international organisation that reports to both the UN General Assembly and the Security Council and is treated as part of the UN system. The Universal Postal Union (UPU) is a long standing intergovernmental organisation responsible for coordinating international postal services and is also a specialised agency of the UN. Therefore, all three statements describing them as UN system agencies are correct, and the only safe choice is the option that says "None of the above" is incorrect, meaning there is no exception.

Step-by-Step Solution:
Step 1: Recognise that the World Bank Group, including IBRD, is listed among specialised agencies formally linked to the United Nations. Step 2: Recall that the International Atomic Energy Agency works closely with the UN and is integrated into the UN system through reporting and cooperation arrangements. Step 3: Remember that the Universal Postal Union is responsible for global postal regulations and is explicitly designated as a UN specialised agency. Step 4: Check each of the first three options: each simply states that these bodies are UN system agencies, which is factually correct. Step 5: Conclude that there is no incorrect statement among the first three, so the correct choice is the one that says "None of the above; all the listed bodies are agencies of the United Nations system."

Verification / Alternative check:
You can confirm this by consulting lists of UN specialised agencies and related organisations. These lists routinely include the World Bank Group, IAEA and UPU, describing how they are linked to the UN through formal agreements or statutes. This provides clear evidence that all three are indeed part of the broader UN family.

Why Other Options Are Wrong:
World Bank is an agency within the United Nations system: This is a correct statement, so it cannot be the answer to a "not an agency" question.
International Atomic Energy Agency is linked to the United Nations: This description is correct because IAEA reports to UN organs and works within the UN framework on nuclear safety and non-proliferation.
Universal Postal Union functions as a United Nations specialised agency: This is also correct; UPU is one of the oldest specialised agencies coordinating postal services worldwide.

Common Pitfalls:
The main trap is to assume that some of these organisations are "independent" and therefore not part of the UN system. While they may have autonomous legal personalities, they are still formally associated as specialised agencies or related organisations. Another pitfall is to focus only on the phrase "not an agency" in the question and overlook that option D clarifies that all three are indeed agencies, turning the question into a test of careful reading.

Final Answer:
Since all the listed organisations are part of the UN system, the correct choice is None of the above; all the listed bodies are agencies of the United Nations system.