In 1554, a cholera outbreak occurred in London. Cholera is a disease that causes intense diarrhea and can be fatal. At the time, many people believed that diseases were caused by “bad air.” John Snow had another idea; he thought that cholera was caused by something in the environment where people lived. He went door to door and made a map showing households that had cholera. He found that most of the cases were near the Broad Street Water Pump. John Snow made a case that the water from the pump was making people sick and the pump was shut down.

REASONING: If water was the cause of the sickness, then …

a) people all over the city would have cholera

b) cholera would be cured with water

c) only people near the pump would have cholera