Concept:The correct answer identifies the area where the Economic Community of West African States has achieved its greatest practical success.
Explanation:ECOWAS was established mainly to promote economic integration among West African countries.
However, its most notable and visible progress is in the area of free movement of persons and right of residence.
The Protocol on Free Movement of Persons, Right of Residence and Establishment was adopted to allow citizens of member states to travel within the region without visas for up to 90 days.
This protocol has made cross-border movement easier and is widely regarded as one of ECOWAS’s major achievements.
Although ECOWAS has introduced a free trade area and a common external tariff to increase trade among members, intra-regional trade has remained relatively low.
Political integration is still limited, and the organisation does not function mainly as a provider of financial aid to members.
Therefore, the greatest progress has been in the free movement of persons and right of residence.
Answer:D. Free movement of persons and right of residence.