Someone please help me with the 4th question only plz!

What causes darkening of the skin as melanin production increases

Will mark brainliest. (20 points) many have pigments structures known as eyespots that detect direction of light. a. b. archaebacteria c. protists d. none of the above

What is a difference between systemic and pulmonary circulation? a. systemic circulation carries oxygenated blood to the lungs and pulmonary circulation carries deoxygenated blood to the body. b. systemic circulation carries deoxygenated blood to the lungs and pulmonary circulation carries oxygenated blood to the body. c. systemic circulation carries deoxygenated blood to the body and pulmonary circulation carries oxygenated blood to the lungs. d. systemic circulation carries oxygenated blood to the body and pulmonary circulation carries deoxygenated blood to the lungs.