Concept:The correct institution is the body specifically set up to improve the trade position of developing countries, including their commodity trade.
Explanation:UNCTAD, the United Nations Conference on Trade and Development, was created to address the trade and development needs of developing countries.
Its main mission includes expanding and diversifying the commodity exports of these countries.
The WTO mainly administers global trade rules and settles trade disputes.
The ECA focuses on promoting economic development within African states.
The AfDB finances development projects and poverty reduction efforts in Africa, not specifically commodity trade expansion.
Thus, the institution directly concerned with expanding developing countries' commodity trade is UNCTAD.
Answer:B. United Nations Conference on Trade and Development (UNCTAD)