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A student smokes a marijuana cigarette during a 'smoke out' with thousands of others April 20, 2010 at the University of Colorado in Boulder, Colorado. (Chris Hondros/Getty Images)

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Pot smokers at the annual 420 celebration in Lincoln Park near the State Capitol in Denver, Colorado on April 20, 2015. (Helen H. Richardson/ The Denver Post)

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Prime Minister Malcolm Turnbull during House of Representatives question time at Parliament House on September 15, 2015 in Canberra, Australia. (Stefan Postles/Getty Images