Explanation:

Manaus, on the banks of the Negro River in northwestern Brazil, is the capital of the vast state of Amazonas. 

Rio de Janeiro is a huge seaside city in Brazil, famed for its Copacabana and Ipanema beaches, 38m Christ the Redeemer statue atop Mount Corcovado and for Sugarloaf Mountain, a granite peak with cable cars to its summit.

Niamey is the capital and largest city of Niger. Niamey lies on the Niger River, primarily situated on the east bank. 

Kinshasa, formerly Léopoldville, is the capital and the largest city of the Democratic Republic of the Congo. The city is situated alongside the Congo River.