Which one of the following is not an example of the consequences of chronic exposure?

a. Over a period of 30 years, workers at a fur felt hat company are exposed to mercury that was used to treat the fur pelts and eventually develop neurological problems as a result of their exposure to the mercury.
b. Japanese citizens living in Hiroshima and Nagasaki when the atomic bombs were dropped develop cancer 35 years later as a result of the large doses of radiation they received when the bombs exploded.
c. Workers involved in the production of electrical capacitors at a General Electric plant in New York are exposed to PCBs over a period of 25 years and develop nervous system disorders as a result.
d. Workers at a nuclear power plant are exposed to low doses of radiation over a period of 20 years develop cancer as a result of their exposure to the radiation.