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  3. The most popular organic gem is the pearl. A pearl is the response of a mari

The most popular organic gem is the pearl. A pearl is the response of a mari

游客2024-01-02  64
问题     The most popular organic gem is the pearl. A pearl is the response of a marine mollusk to the presence of an irritating impurity accidentally introduced into its body; a cultured pearl is the result of the intentional insertion of a mother-of-pearl bead into a live mollusk. Whether introduced accidentally or intentionally, the pearl-making process is the same: the mollusk coats the irritant with a substance called nacre. Nacre is composed chiefly of calcium carbonate. Because very few natural pearls are now on the market, most pearls used in fine jewelry are cultured. These include "Biwa" pearls and most other freshwater pearls. Cultured pearls are not easily distinguished from natural pearls except by an expert. [br] The difference between a pearl and a cultured pearl is the nature of the ______.
选项 A、color
B、introduction of the irritating impurity
C、coating material
D、irritating impurity
答案 B
解析 文章第二句(A pearl is the response of a marine…a live mollusk．)指出：天然珍珠中的刺激性的杂物是偶然进入体内的(accidentally introduced into its body)；而人工培育的珍珠中的杂物是人为加入的(the intentional insertion)；所以选项B正确。
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