The correct answer is D. Kangra.
Wells are the major source of irrigation in Kangra district of Himachal Pradesh. This is because the district has a large number of wells, which are used to irrigate crops. The wells are dug in the ground and are filled with water from the underground aquifers. The water from the wells is used to irrigate crops such as rice, wheat, maize, and vegetables.
The other options are incorrect because they are not the major source of irrigation in Kangra district. Una district is the major producer of wheat in Himachal Pradesh, and the irrigation in the district is mainly done through canals. Kullu district is a hilly district, and the irrigation in the district is mainly done through terraces. Shimla district is a hill station, and the irrigation in the district is mainly done through tanks.