If Cow's Milk Is Found to Contain Unusually High Levels

If cow's milk is found to contain unusually high levels of iodine,what is the most likely explanation?

A) Storage of milk in galvanized tanks
B) Grazing of cows on high-iodine soils
C) Addition of fortified salt at the milk processing plant
D) Exposure of cows to iodide-containing medications and disinfectants