Answer:
D. A unitary government
Step-by-step explanation:
A president who is the head of a government, can be defined as an individual who is duly elected by the electorates and as such is the head of the country in a democratic government. The president is empowered by the constitution to sign (veto) legislations, adjourn or convene the legislative body (Congress), grant state pardons and reprieve to citizens, command the armed forces, and welcome ambassadors representing other countries.
In the United States of America, the president has various powers granted by Acts of Congress and Article II of the U.S constitution such as Ordinance power, Appointment power, Implied power, Executive power etc., and as such is known as a federation because the power of government is dispersed (shared) i.e not centralized.
However, the type of government in which power is centralized is known as unitary government.
A unitary government can be defined as a type of government that has a single supreme authority (power) i.e the authority to govern or rule lies with a centralized government. Some examples of countries that are sovereign states and practices unitary government are United Kingdom (UK), Northern Ireland, France etc.
In conclusion, a unitary government is considered to be the direct opposite of federalism.