The human body contains enough carbon to make nine thousand pencils.
Why it is true
Carbon is one of the most abundant elements in our organism and, if extracted and processed, the amount present in an average adult would be enough to manufacture thousands of graphite leads.
Source: Human Chemistry
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This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.