What is the horizontal and vertical axis of a speed graph

One is speed and the other distance. i think hopefully this helps. 

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.

Ibelieve the answer is d. macula  hope my answer has you : )