A．introduce, in an interesting manner, the discussion of food
B．show the connection between food and nationality of food
C．indicate that there are various ways to prepare food
D．impress upon the readers the food value of fish

A．The writer feels upset that there is no better system of classification than the familiar one of sweet, sour, bitter salty.
B．Psychological perception of the taste is objective because no subject judgment is involved.
C．It is extremely difficult to classify smell, as it's hard to make objective judgment on the stimulus.
D．The classification is subjective, for there is no relation between the perception and the stimulus.