What is one reason a lack of understanding of object permanence can be so upsetting for an infant when his or her caregiver leaves?
a. The infant believes the person has ceased to exist once the person leaves his or her sight.
b. The infant believes the person will be back but does not understand how long it will take.
c. The infant believes the person has chosen to leave because he or she no longer cares.
d. The infant believes the person is completely different and has a new identity once he or she returns