摘要： The underlined word “formula in this passage is referred to A. snow that falls to the ground B. the water coming from the fallen snow C. a set form of words used for daily communications D. a general law or rule used to work a problem out Annealing is way of making metal softer by heating it and then letting it cool very slowly. If metal is heated and then cooled very quickly, for example by dipping it in water, it will be very hard but also very brittle(脆),that is , it will break easily. Metal that has been annealed is soft but does not break as easily. It is possible to make metal as hard or as soft as is wished, by annealing it. The metal is heated, and allowed to cool slowly for a certain length of time. The longer the heated metal takes to cool slowly, the softer it becomes. Annealing can also be used on other materials, such as glass.

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