It's A Charlie Brown Thanksgiving Quiz, Charlie Brown! by RobinJRichards

Question 5

Marcie gives away the biggest secret about Peppermint Patty to Charlie Brown and the world: HER REAL NAME. What is it?

Priscilla (Upon further review, the Priscilla quip was more about the Pilgrim/Charlie and Patty love story and not even a part of her real name. Ergo this and Patricia (Patty) Reinhardt will be accepted.) (edited at 4:00 pm, November 23, 2017 (PST))

Original Answer: Priscilla