a political revolution is

a. a circular course around an axis.

b. a peaceful but sudden change of government.

c. a gradual change in government that eventually brings significant changes to a nation’s people.

d. a violent overthrow of an existing government.

D. A violent overthrow of an existing government.

Explanation:

Political revolution has its origin from the Trotskyist theory. According to this theory, a government can be completely removed or overthrown from its position or some changes can be made in the current government, but all done without affecting the property relations. Two most important events in the world history that are cited as a political revolution were the revolutions in France in 1830 and 1848. The idea behind such a political revolution is to overthrow an undemocratic government which give bureaucratic privileges and thereby replacing such government with democracy; a government that can maintain state-owned property relations.  

.elections are held to determine who serves in congress.

b. the 200th birthday of the united states