Answer: B) protagonist and antagonist.
Step-by-step explanation: in literature, a conflict is a struggle between opposite forces, usually between a character (the main character or a very important one) and himself (internal conflict), society or another character (external conflict). So from the given options, the one that completes the sentence correctly, is the corresponding to option B, so the sentence would be: conflict is the struggle between the protagonist and antagonist in the plot.