<s>[INST] context: .John Snow&;s map of cholera outbreaks from nineteenth century London changed how we saw a disease.John Snow who famously identified a pump as being the source of a cholera outbreak in 1854. Dr. Snow believed sewage dumped into the river or into cesspools near town wells could contaminate the water supply, leading to a rapid spread of disease. In August of 1854 Soho, a suburb of London, was hit hard by a terrible outbreak of cholera. Dr. Snows himself lived near Soho, and immediately went to work to prove his theory that contaminated water was the cause of the outbreak. "Within 250 yards of the spot where Cambridge Street joins Broad Street there were upwards of 500 fatal attacks of cholera in 10 days," Dr. Snow wrote "As soon as I became acquainted with the situation and extent of this irruption (sic) of cholera, I suspected some contamination of the water of the much-frequented street-pump in Broad Street." Dr. Snow worked around the clock to track down information from hospital and public records on when the outbreak began and whether the victims drank water from the Broad Street pump. Snow suspected that those who lived or worked near the pump were the most likely to use the pump and thus, contract cholera. His pioneering medical research paid off. By using a geographical grid to cha deaths from the outbreak and investigating each case to determine access to the pump water, Snow developed what he considered positive proof the pump was the source of the epidemic. [/INST] question: John snow;s discovery of cholera is an example | options: A: Natural experiments B: Spot map study C: Randomized trial D: Sho study | answer: B </s>