The history of transportation is very long and full of changes and inventions. It starts ___46__ walking, which is not any invention; it just takes energy. People used to walk to get to other places. If you wanted to get somewhere quickly, the __47___way to do that was to run . Actually, the first invention for the transportation __48__ was the shoe. Centuries ago there were no shoes, and people walked barefoot.
Then people invented ___49__ to transport themselves and materials from one place to another. In some cultures, people invented sledges(雪橇), ___50__ are a kind of board that you drag along the ground. You can tie things on the sledges to help carry them, but it’s a challenging invention ___51__ if you hit a rock with the sledges as you pull it, the contents can ___52___. In other cultures, people invented the wheels, which they used to make it easier to move things---and people. That was the beginning of many innovations in transportation.
___53___ people had wheels they could invent other ways to travel. They could put the wheels on a board and make it a wagon, and then they could ___54__ that wagon to an ox or a horse and ride as well as carry materials. That wheel led to __55___ we have today: trucks, automobiles, and even boats and planes. For example, there were steamboats that used giant wheels that turned with blades, pushing the water and pushing the boat forward.
46、_________
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