The correct answer is D. Unitary.
Step-by-step explanation
A unitary state is a type of state that is characterized by concentrating power in a single center of authority. However, from the center of power, tasks are delegated and extended throughout the territory of the State through its institutions and local authorities. According to the above, most African states that have a strong central government are unitary because their goverments are characterized for concentrating power in a single center of authority. So the answer is D.