Final answer:
An oligomer is a composition of multiple protein units, typically including dimers, trimers, tetramers, etc., held together by non-covalent interactions. Hemoglobin is an example of an oligomer, being a heterotetramer formed by two α and two β globin polypeptides.
Step-by-step explanation:
An oligomer refers to a molecular complex that is composed of a few (multiple protein units) similar or identical subunits (monomers). They can include dimers, trimers, tetramers, and so on, depending on the number of polypeptides involved.
The subunits in an oligomer are typically held together by non-covalent interactions such as hydrogen bonds, ionic bonds, or Van der Waals forces. An example of oligomers in biology is hemoglobin, which is made of two α and two β globin polypeptides, forming a heterotetramer. Therefore, when we discuss an oligomer in the context of proteins, it is closest to choice C, as it is a composition of multiple, typically small, protein subunits that form a functional unit.