Final answer:
The term for 'a person who actively opposes or is hostile to someone or something; an adversary' is B) Antagonist. An antagonist is the opposing force to the protagonist in a story and is essential to creating conflict.
Step-by-step explanation:
The term for "a person who actively opposes or is hostile to someone or something; an adversary" is B) Antagonist. An antagonist is the character, group, or force that stands in opposition to the protagonist of a story. The antagonist may not always be a villain; it could also be a force of nature, an animal, a societal pressure, or even an internal struggle. The role of the antagonist is crucial in creating conflict and propelling the narrative forward. Characters or forces that support the protagonist are not antagonists; these are allies or supporters. It is also important to note that a protagonist can sometimes be an antihero, who does not necessarily embody traditional heroic qualities.