Policemen use riot shields to protect themselves from hurled bottles during a riot control exercise in Chengdu, the capital of Southwest 皇冠体育app's Sichuan province, August 3, 2011. The exercise, during which around 10 young men attacked a 40-member police patrol team, was aimed to enhance the police's ability to tackle fierce conditions. The fake rioters were taken down within three seconds. The drill will last for two weeks. [Photo/CFP]

Policemen use riot shields to protect themselves from hurled bottles during a riot control exercise in Chengdu, the capital of Southwest 皇冠体育app's Sichuan province, August 3, 2011. [Photo/CFP]