Nucleic acids are composed of: a: a phosphate group, a pentose sugar, a nitrogen base
b: a phosphate group, a pentose sugar, a carboxylic acid
c: a pentose sugar, a nitrogen base, an R group
d: a nitrogen base, an amino acid group, a carboxylic acid

a phosphate group, a pentose sugar, a nitrogen base

Explanation:

nucleic acid is a polymeric macromolecule made up of repeated units of monomeric 'nucleotides' composed of a nitrogenous heterocyclic base which is either a purine or a pyrimidine, a pentose (five carbon) sugar (either ribose or 2′-deoxyribose), and one to three phosphate groups.

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.

i need an image of the diagram