Almosteverymachinewithmovingpartshaswheels,yetnooneknow...
问题详情：Almosteverymachinewithmovingpartshaswheels,yetnooneknowsexactlywhenthefirstwheelwasinventedorwhatitwasusedfor.Wedoknow,however,thattheyexistedover5,500yearsagoinancientAsia. Theoldestkn...