单项选择题

Questions 9 to 12 are based on the conversation yon have just heard.

A. A new fuel for buses.
B. The causes of air pollution.
C. A way to improve fuel efficiency in buses.
D. Careers in environmental engineering.

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单项选择题

Questions 9 to 12 are based on the conversation yon have just heard. 您的浏览器不支持 audio 元素。