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  3. Technological invention has directly or indirectly produced social change in every period of history. The invention of the horse

Technological invention has directly or indirectly produced social change in every period of history. The invention of the horse

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问题     Technological invention has directly or indirectly produced social change in every period of history. The invention of the horse collar in the Middle Ages was a【B1】______technological advance for agriculture; the【B2】______for use at sea so【B3】______navigation in the fifteenth  century that it led in the age of【B4】______; and the steam engine was an【B5】______factor in the industrialization of Europe in the nineteenth century.
    A discovery is another kind of technological【B6】______. While inventions add something  new to a culture, discoveries increase our knowledge of something that already exists. Gravity had always been there, but Newton "discovered" it: be【B7】______how this natural force worked and how its laws【B8】______to falling bodies. This knowledge made possible many new inventions.【B9】______.
    Since each invention makes more inventions possible, the speed of technological development tends to accelerate.  Benjamin Franklin experimented with electricity in the eighteenth century,【B10】______. In the hundred years since Edison invented the light bulb, the discovery  of electricity has led to tens of thousands of inventions, from the internal burning engine to the computer.【B11】______pose some of tile greatest challenges of our time.
【B7】
选项
答案observed
解析 动词，与空格相关的句意为：重力总是存在的，但是牛顿发现了它，他______这个自然力如何起作用以及它的规律如何应用于下落物体。这两个宾语都是要靠观察才能进行，故此处为observe的过去式。
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大学英语四级

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