Concept:Price stability in the international oil market is achieved through cooperation among oil-producing countries.Explanation:The Organisation of Petroleum Exporting Countries, known as OPEC, coordinates oil production policies among member nations.Its major aim is to reduce sharp price fluctuations in the global oil market.By managing output levels, OPEC helps member states earn stable and fair revenue from oil exports.The United Nations, World Trade Organization, and African Union do not have this specific responsibility.Answer:C. OPEC