Models, painted in camouflage colours to blend in with the background, take a walk after practising for posing for Chinese artist Liu Bolin's artwork "Dongji", or Winter Solstice, on the second day after China's capital Beijing issued its second ever "red alert" for air pollution, in Beijing, China, December 20, 2015. In this artwork, Liu wants to express his concerns about China and its people, including air pollution problem, Liu told Reuters. REUTERS/Kim Kyung-Hoon