The correct answer is B. Kuhls.
Kuhls are traditional irrigation channels that have been used in Himachal Pradesh for centuries. They are fed by snowmelt from the Himalayas and are an important source of water for agriculture and drinking water.
Tube wells are also used for irrigation in Himachal Pradesh, but they are not as common as kuhls. Wells are less efficient than kuhls and can be expensive to install.
Option A is incorrect because tube wells are not the main source of irrigation in Himachal Pradesh.
Option C is incorrect because wells are not the main source of irrigation in Himachal Pradesh.
Option D is incorrect because kuhls are the main source of irrigation in Himachal Pradesh.