单项选择题

Questions 22 to 25 are based on the conversation you have just heard.

A．To cheek the accuracy of scales.
B．To see the quality of other metals.
C．To measure changes in the air.
D．To measure the length of metal.

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单项选择题

单项选择题

Questions 22 to 25 are based on the conversation you have just heard. 您的浏览器不支持 audio 元素。