Answer:
A) a scene showing how the bully treated the character in the past
Explanation:
A flasback, in literature and films, is showing events that happened in the past, for some more or less obvious connection to the scene in the present.
If the writer wants to show cause and effect, such is the case here, and if the confrontation is the effect, then we would probably be curious about what events led to this character confronting a bully, what was the cause to that confrontation.
The flashback, then, would probably show som scenes of the bully harassing, beating or mistreating the character in some other way.
