Concept:The largest river in Nigeria is identified by its length and volume of flow.Explanation:The River Niger is the longest and largest river in Nigeria.It takes its source from the Fouta Djallon highlands in Guinea.It flows through several West African countries before entering Nigeria.It is joined by the River Benue at Lokoja, but the Niger remains the main river.None of the other rivers listed is larger or longer than the Niger.Answer:A. River Niger