Justin's Mother Believes That Justin,a Nine-Month-Old,is Still in Piaget's Sensorimotor

Multiple Choice

Justin's mother believes that Justin,a nine-month-old,is still in Piaget's sensorimotor stage of cognitive development.To test this belief,which of the following could she try?

A) see whether he knows how to turn on the TV by using the remote control
B) hide his favorite toy underneath a couch cushion and see whether he looks for it
C) place a brightly colored mobile above his crib and see whether he reaches for it
D) ignore him when he cries and see how long he continues to cry