Which of the following organic molecules is a source of carbon, nitrogen, and phosphorus?
a) calcium carbonate
b)nucleic acids
c)ammonia

structure is maintained and sustained by:

-cytoskeleton: gives cells coherence

-cell wall: support

-cytoplasm: shape

hope this .

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.