Religion centered on the worship of natural forces and exorcism of ghosts and evil spirits. Separate rituals were held by each of the ten or twelve clans. Other rituals concerned community well-being or healing. Able religious leaders spoke Yi, Lisu, and Bai in order to address the spirit-forces of those groups who might be causing illness or other difficulties. Due to the presence of Tibetan Buddhism in the area, some Nu became followers and sent sons to join the lamasaries, where they became literate in Tibetan. Beginning in the late nineteenth century, and particularly from the 1930s on, many of the Nu responded to foreign missionaries and became Catholics or Protestants. In some areas, 60 percent of the population were Christian in the early 1950s. The missionaries introduced modern medical care and opened village schools with Chinese as the classroom language.