Answer:
A nucleotide.
Step-by-step explanation:
DNA and RNA are the polymers of nucleotide or a nucleotide may be considered as a single monomer unit of polynucleotides. These are the building blocks of the nucleic acids.
The structure of nucleotide consists of a pentose sugar, nitrogenous bases and a phosphate group attached with the pentose sugar as depicted in the question diagram. Hence, the given molecule is nucleotide.
Thus, the correct answer is option (D).