Two Students Studying Physiology Taste a Known "Bitter" Substance, and Both

Two students studying physiology taste a known "bitter" substance, and both report sensing bitterness. They then sample another substance. With the new substance, student A reports sensing both a bitter taste and a salty taste, but student B reports only a salty taste. Which of the following best explains the observations from the experiment?

A) Student A had an allergic reaction to the food, causing her to perceive the food as being bitter.
B) Student B has a protein receptor capable of detecting a bitter molecule found in that substance, whereas student A lacks that particular protein receptor.
C) Student A has a protein receptor capable of detecting a bitter molecule found in that substance, whereas student B lacks that particular protein receptor.
D) Student A has normal saliva, whereas student B's saliva is more alkaline than normal.