The answer is "because water is produced as a by-product"...the word dehydration should also be a major clue because that means water loss.
I'm going with C. It may be wrong but I think it's C.
Photosynthesis makes the glucose that is used in cellular respiration to make ATP. The glucose is then turned back into carbon dioxide in the process of respiration, which is then used in photosynthesis. While water is broken down to form oxygen in photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water. ATP is manufactured as a result of several processes including fermentation, respiration and photosynthesis.
