The correct answer is A. Kishanganj.
Kishanganj is a district in the Indian state of Bihar. It is located in the northeastern part of the state, and is bordered by the districts of Araria to the north, Purnea to the east, Katihar to the south, and West Bengal to the west. The district has a population of over 4 million people, and its headquarters is the town of Kishanganj.
Kishanganj is a part of the North Chotanagpur Plateau, and is characterized by its hilly terrain. The district is drained by the Mahananda River, which flows through the district from north to south. The climate of Kishanganj is tropical, with a hot and humid summer and a cool and dry winter.
The main agricultural crops of Kishanganj are rice, wheat, maize, and sugarcane. The district is also home to a number of industries, including sugar mills, rice mills, and textile mills.
Kishanganj is a major tourist destination, and is known for its natural beauty, historical sites, and religious places. The district is home to a number of temples, mosques, and churches.
The following are the details of rainfall in different districts of Bihar:
| District | Average annual rainfall (mm) |
|—|—|
| Kishanganj | 2,000 |
| Araria | 1,800 |
| Saharsa | 1,600 |
| Katihar | 1,400 |
As can be seen from the table, Kishanganj receives the highest rainfall in Bihar. This is due to its location in the northeastern part of the state, which is a part of the North Chotanagpur Plateau. The plateau is characterized by its hilly terrain, which helps to trap moisture from the monsoon rains.