The correct answer is D. Champaran and Muzaffarpur.
The Indigo Revolt of 1866 was a peasant revolt in the Champaran district of Bihar, India. The revolt was led by peasants against the British indigo planters who forced them to grow indigo on their lands. The revolt was successful in ending the indigo contract system and led to the formation of the Champaran Kisan Sabha, a peasant organization that fought for the rights of peasants.
The indigo contract system was a system in which peasants were forced to grow indigo on their lands and sell it to the British indigo planters at a fixed price. The system was exploitative and led to the impoverishment of the peasants. The revolt was a major turning point in the history of India and led to the end of the indigo contract system.
The other options are incorrect because they do not refer to the region of the revolt of an indigo farmer in Bihar in 1866.