Baby billy calls his favorite blanket a "blankie." when he sees other blankets in the house, however, he does not refer to them as a "blankie" because he uses that name only for his favorite blanket. this is an example of ) underextension. b) overextension. c) referential style. d) holophrasic speech.

a) underextension.

Explanation:

Psychologically, underextension can be defined as a classification term used in language to account and relate one object or an entity as opposed to all objects or all entity that is linked to that class. This phenomena is rampant in children when beginning to acquire and reinforce a new language.

In the case of Baby Billy, Baby Billy calls his favorite blanket a "blankie.", he has already  learns the word(blanket) for something else callled (blankie), without extending it to other things in the same category because  when he sees other blankets in the house, he does not refer to them as a "blankie".

answer; philip zimbardo;