Final answer:
The opposite of supination is c) pronation, which is the motion of the forearm that turns the palm downward or backward.
Step-by-step explanation:
The opposite of supination is pronation. Supination and pronation are movements of the forearm. When you supinate, you're rotating your forearm so that your palm is turned upward or forward, much like when you're scooping up soup with a spoon. Pronation is the exact reverse motion, involving the rotation of the forearm so that the palm is turned downward or backward. During pronation, the radius moves around the ulna at the proximal and distal radioulnar joints, bringing the two bones into an X-shape position. This motion is essential for many functional activities involving the hand and arm.