Final answer:
Armin Meiwes posted an advertisement searching for a willing participant for a cannibalistic act. This is reflected in option C) In search of a willing participant. His case is relevant in various fields including sociology, psychology, and law.
Step-by-step explanation:
The question regarding what Meiwes' advertisement said can be answered based on historical accounts. Armin Meiwes posted an advertisement on a website called The Cannibal Cafe which is rumored to have said something along the lines of seeking a willing participant for a cannibalistic act. The most accurate representation of the choices given would be C) In search of a willing participant. Meiwes' case is often studied in the context of legal studies, criminal psychology, and sociological perspectives on deviant behavior.