C. To raise its body temperature after a cool night.
Lizards are cold-blooded animals, which means that they cannot regulate their body temperature internally like warm-blooded animals do. Instead, they rely on external sources of heat, such as the sun, to raise their body temperature and become active. By sunning themselves on a rock in the morning, a lizard can absorb the warmth of the sun and raise its body temperature after a cool night. This allows the lizard to become more active and alert, and better able to find food and carry out other activities throughout the day.