According to the passage, Pfaffman's theory differs from that which has been most recently considered by scientists in that it
A． postulates that peripheral neurons do not respond to a greater extent to stimuli representing a single taste quality
B． ignores the crucial difference between central and peripheral gustatory neurons in their role as mechanisms of taste
C． implies that the activity of any individual taste cell, taken by itself, is ambiguous
D． fails to acknowledge that specific gustatory neurons are associated with particular tastes
E． relies primarily upon research data that has come from human, rather than animal, subjects