The correct answer is option 2: A-4, B-1, C-2, D-3. This option correctly matches each agency with its respective headquarters.

A. United Nations Development Programme (UNDP): The headquarters of UNDP is in New York, denoted by 4 in the list. So, A matches with 4.

B. United Nations Environment Programme (UNEP): The headquarters of UNEP is in Nairobi, denoted by 1 in the list. So, B matches with 1.

C. United Nations Industrial Development Organization (UNIDO): The headquarters of UNIDO is in Vienna, denoted by 2 in the list. So, C matches with 2.

D. Universal Postal Union (UPU): The headquarters of UPU is in Berne, denoted by 3 in the list. So, D matches with 3.

The other options incorrectly match the agencies with their headquarters.