Which of the following describes a response to external stimuli? a a rabbit runs away from a fox that is chasing it b a women drinks water when she is thirsty c a boy eats food when he is hungry d a person yawns when oxygen levels in the blood are low

Does anyone have an answer to this question? if so me.

Check all that occur during ventricular systole. a. the av valves open to allow blood to enter the ventricles from the atria. b. the av valves open to allow blood to enter the ventricles from the atria. c. the semilunar valves remain closed throughout systole to prevent backflow of blood into the ventricles. d. the semilunar valves remain closed throughout systole to prevent backflow of blood into the ventricles. e. the semilunar valves open to allow blood to flow into the large arteries. f. the semilunar valves open to allow blood to flow into the large arteries. g. the av valves close to prevent backflow of blood into the atria.

Explain why many people are concerned about uv rays? explain what causes the skin to burn in the sun? explain why people should avoid the sun if taking a photosensitive medication?