Concept:The highest decision-making organ of ECOWAS is the Authority of Heads of State and Government.Explanation:This organ consists of the heads of state and government of all member countries in the sub-region.It holds the supreme authority over all other ECOWAS institutions.The chairman of this body is elected from among the heads of state and serves for one year.Therefore, it ranks above the Council of Ministers, the Executive Secretariat, and the Defense Council.Answer:A. Authority of Head of State and Government