How do vaccines protect humans from diseases according to paragraph 2? What does the example of the smallpox vaccine illustrate

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问题 How do vaccines protect humans from diseases according to paragraph 2?
What does the example of the smallpox vaccine illustrate?

选项 A、The way that vaccines protect people from diseases.
B、The effectiveness of vaccines in eradicating certain diseases.
C、The practical use of a vaccine to control an epidemic disease.
D、The possible negative outcome of administering vaccines.

答案D

解析 细节分析。在文章的第三段第三句说明:天花疫苗的情况就是这样,该疫苗试图消灭曾一度席卷全美土著居民的天花传染病,却造成大量移民死亡。事实上,本句是对上文的举例说明:在整个接种过程中还有隐患。
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