Answer:
D. After some soul-searching and introspection, Peter knew that it was time for him to move on.
Step-by-step explanation:
Introspection means a reflection looking inward; an examination of one's own thoughts and feelings.
The only sentence that deals with someone reflecting on themselves is D.
Sentence A would be perspective, Sentence B would be criticism, and Sentence C would be inspection.
Hope that helps.