You are throwing a ball straight up in the air. At the highest point, the ball's acceleration is nonzero, but its velocity is zero.
velocity and acceleration are both nonzero.
velocity is nonzero but its acceleration is zero.
velocity and acceleration are zero.

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.