Both Freud and Piaget Described Stages in Children's Development

Both Freud and Piaget described stages in children's development. What was the main difference in the ways they discovered these stages?

A) Piaget studied older children than Freud did.
B) Piaget actually watched children; Freud did not.
C) Freud dealt with children's intellect while Piaget dealt with their emotions.
D) Piaget used a cross-sectional method while Freud used a longitudinal method.