Scientists lit a cave of natural gas on fire in 1971 expecting it to only burn for a few days; it still burns to this day. It has been nicknamed "The Door to Hell".
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A blind American man taught himself to navigate using echolocation. His hobbies include hiking and mountain-biking, and he has now trained over 500 students in his ‘tongue-click’ technique.
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Between 2007 and 2012, Bill Gates gave away $28 billion; saving 6 million lives.
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