Answer:
C. Nucleotide
Explanation:
There are four types of biological molecules existing in nature. These are: carbohydrates, proteins, lipids, and nucleic acids. Nucleic acids are biological polymers made up of monomeric units called NUCLEOTIDES.
A nucleotide as depicted in the attached image is a molecule made up of three components namely; Penrose sugar, phosphate group, and nitrogenous base (adenine, guanine, cytosine and thymine). Based on the image in this question;
A represents ADENINE
S represents SUGAR
P represents PHOSPHATE GROUP
Hence, the monomer is a NUCLEOTIDE.