 Complete the following phrase:  In Sichuan province, in an area incorporating the traditional Tibetan areas Kham and Amdo, Tibetan monks and police clashed in riots on 16 March in Ngaba county Aba after the monks staged a protest. It formed part of the 2008 Tibetan unrest and was one of two major events to happen in Sichuan during 2008, the other being the 