Lilianne is beginning to develop a fear of strangers and will reach for her mother when she sees someone who is unfamiliar.It is likely that Lilianne has also just

A) mastered the principle of conservation.
B) overcome the limitation of egocentrism.
C) developed a sense of object permanence.
D) lost her sense of secure attachment.

Lilianne's fear of strangers and reaching for her mother when she sees someone unfamiliar indicates that she is in the sensorimotor stage of development, which typically ends around age 2. During this stage, infants develop a sense of object permanence, understanding that objects (including people) continue to exist even when they cannot be seen, heard, or touched. This cognitive development milestone is likely related to her new fear of strangers, as she now understands that people she doesn't recognize are different from her primary caregivers. The principle of conservation and overcoming egocentrism are milestones of the preoperational stage (ages 2-7), and losing a sense of secure attachment is not directly related to the development of object permanence.