The Nurse Epidemiologist at a Local Health Department Receives a Report

The nurse epidemiologist at a local health department receives a report that a number of children have elevated lead blood levels. She rules out a number of possible reasons and begins to focus on the local water supply because there had been a change in the water supply. She contacts the epidemiologists that worked on the Flint, Michigan, event. They recommended that she follow the steps they took in their investigation. Their investigation included examining these phases related to the exposure:

A) Prior to the switch, after the switch to the Flint River, after the boil advisory, and after the switch back to the original water source.
B) After the switch to the Flint River, after the boil advisory, after the switch back to the original water source, and after the public health alert.
C) Prior to the switch, after the switch to the Flint River, and after the switch back to the original water source.
D) Prior to the switch, after the boil advisory, and after the switch back to the original water source.