What Is One Way in Which Bitter Receptors Differ from Sour

What is one way in which bitter receptors differ from sour or salty receptors, and what is one consequence for our experience?

A) Bitter receptors are located only at the very back of the tongue; therefore we do not taste a bitter chemical until we are already about to swallow it.
B) The tongue has many kinds of bitter receptors; consequently most of us do not detect very low concentrations of a bitter chemical.
C) Bitter receptors develop gradually as we age; therefore adults reject many foods that infants and children find acceptable.
D) Bitter receptors are heat-sensitive; consequently almost any food tastes bitter if it is hot enough.