Concept:Military decrees can alter the structure of government.Explanation:Decree 34, signed by General Aguiyi Ironsi, abolished Nigeria's federal system.It replaced the regional governments with a unified central administration.This means all power was concentrated in the central government.Such a system, where the central authority is supreme, is called a unitary system.Therefore, Decree 34 introduced the unitary system of government.Answer:A. unitary