Which Action Demonstrates Piaget's Formal Operations Period of Development

Multiple Choice

Which action demonstrates Piaget's formal operations period of development?

A) Touching everything and putting everything into the mouth to learn about the surroundings
B) Learning not to touch a hot radiator cover again after suffering a mild burn the first time
C) Taking insulin as prescribed because otherwise dangerous complications of diabetes will develop
D) Understanding that a family vacation is in the future and asking daily if vacation will be "today."