Which of the following is/are a substage(s) of Piaget's sensorimotor cognitive developmental stage?

• A. Primary circular reactions
• B. Secondary circular reactions
• C. Coordination of reactions
• D. All of the above

Answer: (D)

Piaget’s sensorimotor stage unfolds through several substages as infants learn by acting on the world. Primary circular reactions involve repeating actions centered on the infant’s own body. Secondary circular reactions extend this pattern to actions that produce noticeable effects on objects in the environment. Coordination of secondary circular reactions is when the infant combines such actions to achieve a goal, showing more deliberate problem solving and the beginnings of object permanence. Because each of these describes a distinct substage within the sensorimotor period, all of them are included, so the best choice is all of the above.