Which of the following is NOT one of Piaget's four cognitive development stages?

• A. Sensorimotor.
• B. Preoperational.
• C. Concrete Operational.
• D. Existential Operational.

Answer: (D)

Piaget's stages of cognitive development are four universal stages, each marking a distinct way of thinking. The four recognized stages are sensorimotor, preoperational, concrete operational, and formal operational. An option like existential operational isn’t part of his framework; Piaget never proposed a stage by that name. The term that fits the theory is formal operational, which describes the ability to think abstractly and hypothetically. So the correct choice rests on identifying a term that does not belong to Piaget’s sequence.