Which river was essential to the survival of the

West African kingdoms of Ghana, Mali, and

Songhai?

(1) Thames (3) Indus

(2) Niger (4) Euphrates

Just compare a river map of West Africa to a map of West African kingdoms.

You can clearly see that all of these kingdoms form around the Niger River.

More support to this: None of these other rivers are even in Africa: The Thames is in England, the Indus is in Pakistan, and the Euphrates runs through the Middle East.