The correct answer would be letter C.
Photosynthesis puts oxygen in the atmosphere.
The two differences you see when comparing the four chambers of the heart is that the arteries have a thicker wall and veins have thin walls and that the arteries carry oxygenated blood away from the heart which means they get more pressure than veins.
Inner planets are all of the planets inside the asteroid belt, so that would be Mercury, Earth, Venus, and Mars.
