According to Vygotsky, What Does the Use of Private Speech

According to Vygotsky, what does the use of private speech mean for a child's cognitive development?

A) The child is using language to facilitate his or her own task performance.
B) The child's use of language is a reflection of his or her persistent egocentrism.
C) The child is displaying highly advanced verbal skills, an indication that he or she is intellectually gifted.
D) The child is displaying very delayed verbal skills, indicating that he or she may require remedial education.