Baby Dennis sees a ball on the floor. He picks it up, looks at it carefully, and then bangs it on the ground. He picks it up again, holds it over his head, and drops it. Then, he picks it up and throws it. Dennis continues playing for several minutes. Dennis is in which of Piaget's sensorimotor substages?
a. primary circular reactions
b. secondary circular reactions
c. coordination of secondary circular reactions
d. tertiary circular reactions