Organisms having the potential for interbreeding and producing fertile offspring is called

The correct answer is D. Species.

A species is a group of organisms that can interbreed and produce fertile offspring. Members of the same species share a common ancestor and are similar in appearance and behavior.

A class is a group of related orders. Orders are groups of related families. Families are groups of related genera. Genera are groups of related species.

Therefore, the answer is species.