The correct answer is: a) The birth, enlightenment, and passing of the Buddha.
Saga Dawa is a major Buddhist festival that commemorates the birth, enlightenment, and passing of the Buddha. It is celebrated on the fourth full moon of the Tibetan calendar, which usually falls in May or June. The festival is a time for Buddhists to reflect on the Buddha’s teachings and to make offerings to the Sangha, the community of Buddhist monks and nuns.
Option b) is incorrect because Guru Rinpoche’s (Padmasambhava) arrival in Tibet is commemorated on the 10th day of the 5th month of the Tibetan calendar.
Option c) is incorrect because the victory of good over evil is commemorated on the 10th day of the 12th month of the Tibetan calendar.
Option d) is incorrect because the harvest season is not a major Buddhist festival.