Until the 18th century mankind's output had been restricted by the amount of physical force that humans (and domesticated animals) could exert and by the amount of wood that people could chop down.
直至18世纪前，人类的产出仍受制于人(及家畜)的体力以及砍伐树木的数量。
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This is controlled by unfolding of VWF by blood flow, which then allows an enzyme - called ADAMTS13 - to get into the protein and chop it up.