The correct answer is: a) Rumtek Monastery.
Bumchu, a sacred water festival, takes place mainly at Rumtek Monastery in Sikkim, India. The festival is held every year in the 10th month of the Tibetan calendar, which usually falls in November or December. The festival marks the occasion of Guru Padmasambhava’s descent from the Copper-Colored Mountain with a vase of sacred water. The water is believed to have healing powers and is distributed to the faithful.
Rumtek Monastery is the seat of the Karmapa, the head of the Karma Kagyu lineage of Tibetan Buddhism. The monastery was founded in 1670 by the 12th Karmapa, Chogyam Trungpa Rinpoche. It is one of the largest and most important monasteries in Sikkim.
The other options are incorrect because they are not the main location of the Bumchu festival. Pemayangtse Monastery is located in Pemayangtse, Sikkim. Enchey Monastery is located in Gangtok, Sikkim. Tashiding Monastery is located in Tashiding, West Sikkim.