Which Is a Legitimate Criticism of Vygotsky's Theory

Which is a legitimate criticism of Vygotsky's theory?

A) There is no evidence that private speech helps children solve problems.
B) He placed too much emphasis on the influence of social interactions.
C) His stages of psychosocial development have received little empirical support.
D) A model that focuses only on postformal thinking in adulthood is too limited to be considered a major developmental theory.