Microsoft founder Bill Gates, his wife Melinda French Gates and British Prime Minister David Cameron at the World Economic Forum on January 28, 2011, in Davos, Switzerland. Johannes Eisele/AFP/Getty Images hide caption

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A Dutch man rides his bike by windmills in Kinderdijk, the Netherlands in 2007. Dutch researchers have found that the ability to ride a bike can help doctors distinguish between two similar forms of Parkinson's disease. Evert-jan Daniels/AP hide caption

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A boy with symptoms of cholera waits for treatment at the St. Catherine hospital in Cite Soleil in Port-au-Prince on Nov. 10, 2010. Cholera has sickened more than 91,000 Haitians and killed more than 2,000. Ramon Espinosa/AP hide caption

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Two sisters rest under a mosquito net during a July monsoon rain in Prey Mong kol village in Cambodia's Pailin province. Paula Bronstein/Getty Images AsiaPac hide caption

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