Researchers believe Piaget may have underestimated infant 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 require 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.