Which of the following statements best proves that the law of conservation of mass is obeyed during photosynthesis? a: the starting total number of oxygen atoms in carbon dioxide is equal to the ending total number of oxygen atoms in glucose. b: the starting total number of oxygen atoms in carbon dioxide gas is equal to the ending total number of oxygen atoms in glucose and oxygen. c: the total mass of glucose and oxygen formed from photosynthesis is equal to the total mass of carbon dioxide and water used up during the reaction. d: the total mass of glucose and carbon dioxide formed from photosynthesis is equal to the total mass of oxygen and water used up during the reaction.