Calvin,who Is Trying to Impress His Psychology Professor with His

Calvin,who is trying to impress his psychology professor with his knowledge of infant motor development,asks why some infants learn to roll over before they lift their heads from a prone position,while others develop these skills in the opposite order. What should Calvin's professor conclude from this question?

A) Calvin clearly understands that the sequence of motor development is not the same for all infants.
B) Calvin doesn't know what he's talking about. Although some infants reach these developmental milestones ahead of others,the order is the same for all infants.
C) Calvin needs to be reminded that rolling over is an inherited reflex,not a learned skill.
D) Calvin understands an important principle: Motor development is unpredictable.