Based on the passage which is the greatest reward to get a job on a steam boat

Like a horror movie, throughout the first half of the 20th century, the polio virus arrived each summer, striking without warning. No one knew how polio was transmitted or what caused it. There were wild theories that the virus spread from imported bananas or stray cats. There was no known cure or vaccine.

Explanation:

1894, first outbreak of polio in epidemic form in the U.S. occurs in Vermont, with 132 cases. 1908, Karl Landsteiner and Erwin Popper identify a virus as the cause of polio by transmitting the disease to a monkey.

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