Edgar can sound out most three-letter words, but when he sees a long eight-letter word, he turns to his teacher instead of trying to sound it out. His teacher encourages him to go ahead and try to sound it out by breaking it down into two parts. According to Vygotsky, Edgar:______.
a. is in the zone of proximal development.
b. is engaged in egocentric speech.
c. is developing his fast-mapping skills.
d. needs to practice his language overregularization