Facebook founder Mark Zuckerberg has denied that untrue stories appearing on the social media site affected the results of the American presidential election. In a Facebook post, Zuckerberg said many people were questioning whether fake news had influenced the election results. He said he takes such questions seriously and that Facebook has a responsibility to try to prevent fake stories from spreading. Last week, businessman Donald Trump became president-elect of the United States after defeating former Secretary of State Hillary Clinton. The voting was very close. Many opinion surveys in the days before the election had predicted that Clinton would win. Zuckerberg said that, of all the stories and other content posted on Facebook, about 99 percent of what people see is real. Only a very small amount is fake news and hoaxes.