填空题
| Man’s first real invention, and one of
the most important inventions in history, was the wheel. All transportation and
every machine in the world depend on it. The wheel is the simplest yet the most remarkable of all inventions, because there are no wheels in nature—no living thing was ever created with wheels. How, then did Man come to invent the wheel Perhaps some early hunters found that they could roll the dead body of a heavy animal through the forest on logs more easily than they could carry it. However, the logs themselves weighed a lot. It must have taken a great prehistoric thinker a long time to imagine two thin pieces of log collected at their centers by a strong stick. This would roll along just as the logs did, yet it would be much lighter and easier to handle. Thus the wheel and the axle came into being, and with them the first carts were invented. |