Concept:This question tests knowledge of Nigeria’s early diplomatic history at the United Nations.Explanation:Nigeria joined the United Nations shortly after independence in 1960.Chief Samuel Adebo was appointed as Nigeria’s first Permanent Representative to the UN.He represented Nigeria during the country’s early years of international engagement.General Joseph Garba, Professor Ibrahim Gambari, and Alhaji Yusuf Maitama Sule all served at the UN later, not first.Thus, the correct pioneer diplomat is Chief Samuel Adebo.Answer:A. Chief Samuel Adebo