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  3. It is only a shiny, yellow metal, but it is one of the most valuable metals on earth. Since the beginning of time, men have look

It is only a shiny, yellow metal, but it is one of the most valuable metals on earth. Since the beginning of time, men have look

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问题     It is only a shiny, yellow metal, but it is one of the most valuable metals on earth. Since the beginning of time, men have looked for this extremely valuable item, gold.
    Gold is soft and easy to form into different objects. If it gets wet, it does not rust like iron or other metals. Acids do not change it. One important reason that gold is so valuable is that it is scarce.
    Due to its softness, gold must be combined with other metals to harden it and give it strength. By hardening gold, people can then make coins and jewelry with it. Metals commonly mixed with gold are nickel, platinum, and copper. Gold jewelry bears a number and the letter K. The K means karat(carat), which is a measure of the amount of pure gold in the jewelry. Pure gold is 24K. Therefore, a necklace which is 14K is fourteen parts gold and ten parts other metal.
    Many countries utilize gold for certain coins, but this practice is not as common now as it once was. The United States, for instance, stopped making gold coins in 1933.
If a ring is marked 12K, then the percentage of gold in it is______.
选项 A、12
B、50
C、25
D、24
答案A
解析 细节题。问题问一戒指标为12K，那么它的黄金含量是多少。文中第三节的倒数第二行说到纯金为24K，我们不难算出其黄金含量是12＼24，换算一下，即：50％，故选B。
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