单项选择题

Questions 14 to 17 are based on the following passage. At the end of the passage, you will be given 20 seconds to answer the questions. Now listen to the passage. The first permanent picture was made by using

A．special paper
B．silver salt
C．common salt
D．a special metal

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单项选择题

单项选择题

Questions 14 to 17 are based on the following passage. At the end of the passage, you will be given 20 seconds to answer the questions. Now listen to the passage. The first permanent picture was made by using 您的浏览器不支持 audio 元素。