单项选择题

Questions 14-16 are based on the following monologue introducing the development of vaccines. You now have 15 seconds to read Questions 14-16.
What was the first step in fighting against infectious disease

A．The discovery of a vaccine.
B．A powerful injection.
C．The help of a milkmaid.
D．The help from government.

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单项选择题

单项选择题

Questions 14-16 are based on the following monologue introducing the development of vaccines. You now have 15 seconds to read Questions 14-16. What was the first step in fighting against infectious disease 您的浏览器不支持 audio 元素。