Based on Material Presented in the Text, Which of the Following

Based on material presented in the text, which of the following children shows the most cognitive maturity?

A) Sandy, who whispers to herself as she solves a challenging math problem.
B) Shannon, who used to use private speech but now rarely does, because this speech has become internalized.
C) Susan who has a learning problem and relies on private speech.
D) Soraya, who does not seem to use private speech, because she has been punished for making too much noise when she talks to herself.