According to B.F. Skinner, when parents require that children's utterances of words be progressively closer to actual words before they are reinforced, this is called

A) grammatical construction.
B) expressive vocabulary.
C) shaping.
D) negative reinforcement.

Shaping is a process described by B.F. Skinner where reinforcements are given for progressively closer approximations to a desired behavior. In the context of language acquisition, this means parents reinforce sounds that more closely resemble actual words over time, encouraging the development of speech.