_________________________ showed us some important things to look for in cognitive development,such as the shift from preoperational to concrete-operational thinking.

A) Vygotsky
B) Freud
C) Skinner
D) Piaget

Piaget's theory of cognitive development includes the concept of stages of development, including the preoperational and concrete-operational stages. Therefore, Piaget is the best choice for the given statement. Vygotsky's theory emphasizes the role of social interaction in cognitive development, while Skinner's theory focuses on behaviorism and conditioning. Freud's theory pertains to psychosexual development.