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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2025-02-03  14
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] Cultured pearl is formed by ______.
选项 A、insertion of a pearl into a live mollusk
B、an oyster into which a piece of grit has been placed
C、putting in a live mollusk
D、placing a bead into culture
答案 B
解析 文章第二句(…a cultured pearl is the result of the intentional insertion of a mother- of-pearl bead into a live mollusk．)指出：人工培育的珍珠是在活的贝类中人为加入珍珠母珠(the intentional insertion of a mother-of-pearl bead)：所以选项 B．an oyster into which a piece of grit(粗沙)has been placed正确。
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