In a tragedy,the one who opposes the protagonist is the A.antagonist B.postagonist C.pretagonist

A. antagonist

Extra: In literature and drama, particularly in a tragedy, characters play specific roles in the storyline. The protagonist is the main character who drives the story forward and is often considered the "hero" of the narrative. This is the character that the audience is meant to empathize with or root for. On the other side, the antagonist is a character who opposes the protagonist. The antagonist is often considered the "villain" or the opposing force that creates conflict for the protagonist. The antagonist is not necessarily evil; their goals or desires just conflict with those of the protagonist.

In contrast, the terms "postagonist" and "pretagonist" you mentioned are not standard terms used in the analysis of literature. It appears they could be typos or misunderstandings of the correct terms. Understanding the roles of protagonist and antagonist is crucial as they represent the central conflict around which most stories revolve. This conflict is vital to the plot and often leads to key moments of drama, providing the emotional and narrative tension that keeps the audience engaged.