You want to use radioactively labeled oxygen to trace carbon fixation in a plant. you should incorporate the radioactively labeled oxygen into:

a) co2
b) h2o
c) c6h1206
d) o2

the man is bald so he has no hair to get wet

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.