Concept:The Niger Basin Commission focuses on the joint management and development of the River Niger's resources.
Explanation:The commission was set up to improve cooperation among the countries that share the River Niger.
Its main objectives include promoting navigation on the river, controlling floods and erosion, and encouraging studies on the river's agricultural potential.
It also aims to streamline the construction of dams on the Niger so the river's water is used effectively.
These objectives relate to resource management, not to border controls, tariffs, or general cargo movement.
Therefore, the correct objective from the given options is streamlining the construction of dams on the river.
Answer:D. streamlining the construction of dams on the river.