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.
What was De Forest’s most famous device

A．Telephones.
B．Electron tube.
C．Long wave radio broadcasts.
D．Shortwave radio broadcasts.

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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. What was De Forest’s most famous device 您的浏览器不支持 audio 元素。