Which of the following does not represent a commonality in Piaget's and Vygotsky's theories of cognitive development?

a. Both Piaget and Vygotsky argue that appropriate challenge is beneficial for children's development.
b. Both Piaget and Vygotsky suggest that, at any given point in their development, children may be ready for some experiences, but others remain out of reach.
c. Both Piaget and Vygotsky recognize that children's thinking processes become more complex with age and experience.
d. Both Piaget and Vygotsky maintain that cognitive development is the result of children's own efforts.