Final answer:
Kimberly's inability to remember an embarrassing event at her friend's birthday party is an example of repression. Therefore, the correct option is A.
Step-by-step explanation:
In this case, Kimberly's inability to remember a embarrassing event from her friend's birthday party is an example of repression. Repression is a defense mechanism in which anxiety-provoking memories are blocked from conscious awareness. In Kimberly's case, the embarrassing memory is too overwhelming to deal with, so it gets repressed and removed from conscious awareness.