According to a a poll from 2004 by CNN involving more than 10.600 people. 89% believe there is a US government cover-up surrounding 9/11.
http://www.911truth.org/cnn-online-poll-89-believe-theres-been-a-911-cover-up/
This is about another poll from 2013: “After seeing video footage of Building 7′s collapse: 46% are sure or suspect it was caused by controlled demolition, compared to 28% who are sure or suspect fires caused it, and 27% who don’t know.”
http://rethink911.org/news/new-poll-finds-most-americans-open-to-alternative-911-theories/
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In France. The results are mirrored by a HEC poll published in 2011 showing that 58% have doubts compared to 31% percent who accept the official story. Half of the ones who have doubts suspect that US authorities deliberately allowed the attacks to take place, while a third suspect they were actively implicated in the execution of 9/11.
In the UK, only 8% fully agree they have been told the real story of the 9/11 attacks. Of those who expressed an opinion 37% agreed that rogue elements in the American intelligence services may have made a decision prior to 9/11 to allow a terrorist attack to take place.
http://www.reinvestigate911.org/content/911-opinion-poll-majority-doubt-official-911-story
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In France… 56% say the Sun gravitate around Earth…
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From CNN in 2006, 33% of the American think it is an inside job.