Hannah is playing with her 7-month-old niece, Ellie. She rolls a toy truck toward her and Ellie tries to roll it back. One time
the truck rolls behind a chair and is out of sight. Ellie seems to forget about the truck and about the game they had both enjoyed playing. This is because Ellie has not achieved_______.a. conservationb. sensorimotor memoryc. object permanenced.d.egocentrism
