2. 外语
  3. Several of the chemical elements were known in prehistoric【C1】______ . One of the great【C2】______ forward in civilization came w

Several of the chemical elements were known in prehistoric【C1】______ . One of the great【C2】______ forward in civilization came w

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问题     Several of the chemical elements were known in prehistoric【C1】______ . One of the great【C2】______ forward in civilization came when bronze, an alloy,【C3】______ stone as the main material for tools and weapons. The iron replaced bronze. The first elements【C4】______ were those that were found free in nature or could be readily【C5】______ from their ores at relatively low temperatures. During the Middle Ages, chemistry was mostly practised by the alchemists,【C6】______ tried to turn base metals into gold, and who were interested in discovering a way of living for【C7】______ . But they discovered many important【C8】______ about the metals and some of the most easily attainable compounds. Even before the Middle Ages, people knew how to【C9】______ mercury, tin, and iron from their ores. By the time of Paracelsus, chemistry was developed largely to the effort of【C10】______ medicines.
【C2】
选项 A、step
B、steps
C、pace
D、paces
答案B
解析 step作名词是"步伐，步子"的意思，它也可作抽象名词。在短文中，one of…之后的名词用复数，因此选B。C项pace一般不用于表达抽象概念。
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