Smarty's Ball Has Rolled Under the Sofa, and He Immediately

Multiple Choice

Smarty's ball has rolled under the sofa, and he immediately starts to hunt for it. Smarty's behavior illustrates

A) that one must know decentering in order to conserve.
B) the boundaries of his zone of proximal development.
C) that he is in Piaget's formal operations stage
D) the Piagetian principle of object permanence.