The correct answer is A. Sitamarhi.
Piedmont soil is a type of soil that is found in the piedmont region, which is the area at the foot of a mountain range. This type of soil is characterized by its high content of clay and silt, which makes it well-drained and fertile. Piedmont soil is found in many parts of the world, including the United States, Europe, and Asia.
In Bihar, piedmont soil is found in the districts of Sitamarhi, East Champaran, West Champaran, and Araria. These districts are located in the northern part of the state, and they are characterized by their rolling hills and fertile plains. The piedmont soil in these districts is ideal for growing a variety of crops, including rice, wheat, and maize.
The other options are incorrect because they are not districts in Bihar where piedmont soil is found. Option B, East Champaran, is a district in Bihar, but piedmont soil is not found there. Option C, West Champaran, is also a district in Bihar, but piedmont soil is not found there either. Option D, Araria, is a district in Bihar, but piedmont soil is not found there either.