Unlike Sweet, Salty, Sour, or Umami, the "Bitter" Category of Tastants

Unlike sweet, salty, sour, or umami, the "bitter" category of tastants includes wide structural variety of detected molecules. Multiple receptors are required to sense the different bitter tastants. What do they have in common? Bitter taste is thought to have evolved as a warning system for toxic compounds.
-The bitter receptor hTAS2R38 is activated by glucosinolates found in plants such as turnips and broccoli. Glucosinolates can block synthesis and transport of iodine. Before the advent of iodized salt, this was a particular problem in areas of the world that are naturally low in iodine. Why might the human population include different variants of the hTAS2R38 gene?

A) Areas of high iodine are generally coastal, and turnips and broccoli are not easily grown there.
B) Iodine created mutations in the hTAS2R38 gene.
C) Where iodine was low, eating plants rich in glucosinolates helped people metabolize iodine, but where iodine was high they avoided such foods.
D) Where iodine was low, it was important to avoid foods with glucosinolates, but where iodine was plentiful, palatability of a wider range of plants was beneficial.