题目内容：

In many people's opinion, man's first real invention,1.is also one of the most important inventions in history, 2. (be) the wheel. All transportation and every machine in the world depend3.it. The wheel is the4.(simple) yet perhaps the most remarkable of all5.(invention) because there are no wheels in nature. How, then, did man come to invent the wheel? Perhaps some early hunters6. (find) that the body of a heavy animal could be rolled through the forest on logs (圆木) more7. (easy) than they could carry it. However, the logs 8. (them) weighed a lot. It must have taken 9. great prehistoric thinker to imagine two thin slices of log connected at their centers by a strong stick. This would roll along just as the logs did, yet be much lighter and easier10. (handle). Thus the wheel and axle(车轴) came into being and with them the first carts.