2. 外语
  3. Refrigeration (冷藏) is one of the most important means of keeping food. Refrigeration makes anything cold. Scientists and enginee

Refrigeration (冷藏) is one of the most important means of keeping food. Refrigeration makes anything cold. Scientists and enginee

admin2009-07-28  63
问题    Refrigeration (冷藏) is one of the most important means of keeping food. Refrigeration makes anything cold. Scientists and engineers have discovered many means of making things cold.
   One way is to allow water, or another liquid, to evaporate (蒸发). Evaporation cools a liquid and the liquid cools the food.
   Cold can also be produced by passing a gas through a small hole. Gases are made up of molecules (分子). Before the molecules pass through the small hole, they are close together. They are also moving quickly. Afterwards they are further apart and moving more slowly. Because the molecules are moving slowly, the gas is cool. The slower the molecules move, the cooler the gas will be. If the molecules move very slowly the gas changes into a liquid. Liquid oxygen can be made by passing it through a small hole.
选项 A、a liquid to move slowly
B、a liquid to evaporate
C、a gas to evaporate
D、a molecule to move slowly
答案B
解析 此题题干问制冷的一种方法。在原文第2段可以得出蒸发可以让液体变冷。因此选项B. a liquid to evaporate是正确答案。
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