Students stand behind as a policeman and a teacher try to defend them against an intruder during an anti-violence exercise at a primary school in Jinan, Shandong province, December 18, 2012. The exercise was held four days after last Friday's knife attack at a primary school in Henan province, leaving more than 20 children and an elderly villager injured. Picture taken December 18, 2012. REUTERS/China Daily (CHINA - Tags: CRIME LAW EDUCATION) CHINA OUT. NO COMMERCIAL OR EDITORIAL SALES IN CHINA
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