试题与答案

天气预报中“明天的降水概率为20%”,表示明天[ ] A.一定下雨 B.不可能下

题型:选择题

题目:

天气预报中“明天的降水概率为20%”,表示明天  [ ]

A.一定下雨    

B.不可能下雨 

C.下雨的可能性很小

答案:

答案:C

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题型:单项选择题

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 free 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.

Nacre is a substance that is ______.

A.mechanically manufactured

B.the result of laboratory testing

C.organically secreted by the mollusk

D.present in the chemical composition of freshwater pounds

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