What effect did the flu virus have on
healthy young men and women in
1918?

The 1918 pandemic was unusual in that it killed many healthy 20- to 40-year-olds, including millions of World War I soldiers. In contrast, people who die of the flu are usually under five years old or over 75. The factors underlying the virulence of the 1918 flu are still unclear.

Explanation:

the answer is d. selective incorporation. (apex)

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