It is for this reason that men began putting burdens on the backs of mules instead of on their own;that they went on to invent the wheel and the wagon, the railroad and the motor truck.

• 也正是由于这一原因，人们着手用畜力代替人力负重，并且进一步发明了轮子和四轮马车，发明了铁路和载货汽车。