From Vygotsky's Perspective, What Important Role Does Inner Speech Play

From Vygotsky's perspective, what important role does inner speech play?

A) By giving themselves directions about what to do next, children guide themselves through complex tasks.
B) By using words mentally as well as orally, children develop more abstract representations of the world.
C) By practicing various grammatical structures mentally, children acquire more complex language capabilities.
D) By talking to themselves about what they should have done or said in a particular situation, children remember the situation more vividly.