In which stage of photosynthesis is the water used, in which stage of photosynthesis is the carbon dioxide used, in which stage is the oxygen released?

the sphincter muscles at the end of the digestive tract is the anus.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.