According to Vygotsky, How Does a Preschooler's Private Speech Change

According to Vygotsky, how does a preschooler's private speech change over time?

A) It becomes even more overt during later childhood, serving as the basis for effective interpersonal communication.
B) It persists at about the same level throughout childhood.
C) It disappears completely when children enter the early elementary school years.
D) It persists, but becomes increasingly silent, covert speech.