An apology provides the best chance of repairing a seriously damaged relationship.
The correct answer is option C. "An apology".
Most of the close interpersonal relationships that are damaged by misunderstanding the other people's point of view or not accepting when an mistake has done. On 2015 JT Lewis' article "Apologies in Close Relationships: A Review of Theory and Research", a review of eight studies examining predictors of the occurrence and effectiveness of apologies was performed. The results associated positive relationship outcomes when the transgressor apologized, particularly when the apology was related with adopting a self-focus or self-other focus.
b. is correct just got it right.