The correct answer is D. He provides exposition about action in the scene.
Shakespeare's use of stage directions in this excerpt sets the stage for the conflict between the characters, indicating that a fight is about to occur and that tensions are high. The actions of Benvolio trying to separate the fighters, and Tybalt's aggressive challenge, give insight into the current state of affairs in the plot without providing resolution, past occurrences, or predictions about the conclusion of the story.