Nucleotide Composition Steps:

• Recall that a nucleotide is the basic unit of nucleic acids like DNA and RNA.
• Identify core components: a nitrogenous base, a five-carbon sugar, and one or more phosphate groups.
• Assume 1–4 refer to common options (e.g., 1: amino acid, 2: lipid, 3: sugar + phosphate, 4: nitrogenous base).
• Match D (3 and 4) to the essential parts: sugar-phosphate backbone and base.

Why D is correct:

• Nucleotides consist of a nitrogenous base (purine or pyrimidine) and a sugar-phosphate group, as defined in molecular biology.

Why the others are wrong:

• A includes non-nucleotide elements like lipids or amino acids.
• B pairs irrelevant components, excluding the base.
• C omits the phosphate, which links nucleotides in polymers.

Not enough information to confirm exact labels for 1–4.

Final answer: D