Tibet:

Religion is extremely important to the Tibetans and has a strong influence over all aspects of their lives. Bön is the ancient religion of Tibet, but has been almost eclipsed by Tibetan Buddhism, a distinctive form of Mahayana and Vajrayana, which was introduced into Tibet from the Sanskrit Buddhist tradition of northern India. Tibetan Buddhism is practiced not only in Tibet but also in Mongolia, parts of northern India, the Buryat Republic, the Tuva Republic, and in the Republic of Kalmykia and some other parts of China. During China's Cultural Revolution, nearly all Tibet's monasteries were ransacked and destroyed by the Red Guards. A few monasteries have begun to rebuild since the 1980s (with limited support from the Chinese government) and greater religious freedom has been granted – although it is still limited. Monks returned to monasteries across Tibet and monastic education resumed even though the number of monks imposed is strictly limited. Before the 1950s, between 10 and 20% of males in Tibet were monks.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". When were nearly all of Tibet's monasteries destroyed by the Red Guard?
During China's Cultural Revolution