Community a Receives Its Water from Several Sources

Community A receives its water from several sources. The water source responsible for causing an outbreak of disease X is unknown. The best evidence to determine which suspected water supply is responsible would be:

A) the identity of the water supply providing water to the largest proportion of cases.
B) the relationship between quantity of water consumed and the severity of attack for each individual.
C) the identity of the water supply that has the greatest opportunity for contamination during the epidemic.
D) the attack rates for disease X in those who did and did not drink from each water supply.