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  3. The invention of both labor-saving tools and tools of intelligence is rarely accidental. Instead, it is usually the product of h

The invention of both labor-saving tools and tools of intelligence is rarely accidental. Instead, it is usually the product of h

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问题     The invention of both labor-saving tools and tools of intelligence is rarely accidental. Instead, it is usually the product of human need;【C1】______is truly the mother of invention. People usually devise tools to【C2】______for natural deficiencies. For example, people invented weapons to defend【C3】______from physically superior【C4】______. But【C5】______is only one incentive for inventions. People also invent【C6】______tools to【C7】______certain established tasks more efficiently. For instance, people developed the bow and arrow from the【C8】______spear or javelin in order to shoot【C9】______and strike with greater strength.
   【C10】______civilizations developed, greater work efficiency came to be demanded, and【C11】______tools became more【C12】______. A tool would【C13】______a function until it proved【C14】______in meeting human needs, at which point an improvement would be made. One impetus for invention has always been the【C15】______for speed and high-quality results — provided they are achieved【C16】______reasonable costs. Stone pebbles were sufficient to account for small quantities of possessions,【C17】______they were not efficient enough for performing sophisticated mathematics. However, beads arranged systematically evolved into the abacus. The【C18】______of this tool can be【C19】______to the development of commerce in the East around 3000 B.C., and the abacus is known【C20】______by the ancient Babylonians, Egyptians, Chinese, etc..
【C20】
选项 A、to be used
B、to have used
C、to have been used
D、to use
答案C
解析 本题测试语法。本句话表示在过去的时间里已经完成的动作或存在的状态，所以应该用完成时态。B的语态不对。应该选C。
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