Researchers Believe Piaget May Have Underestimated the Infant's Understanding of Object

Researchers believe Piaget may have underestimated the infant's understanding of object permanence because

A) the items Piaget expected infants to find were not interesting to babies.
B) his means of assessing object permanence required that infants have sufficient motor skills to search for objects and lift barriers.
C) he did not include young infants in his studies.
D) his measures of object permanence required that the infants use language to indicate where the hidden objects were located.