HONG KONG (Reuters) -Police deployed in the streets of Hong Kong in large numbers on Thursday to prevent protests on the anniversary of its return to Chinese rule as its acting leader said last year's national security law had restored order after a period of chaos. Police vans, water cannon trucks, armoured vehicles and police units patrolled the streets. Passers-by were stopped and searched, with at least 20 people arrested. One man died after stabbing a police officer with a knife. Police and hospital spokespersons were unable to give details on how he died. The policeman was taken to hospi...