Question: Zulema Castro de Peña was a member of what organization that began to march in 1977 at the Plaza de Mayo in Buenos Aires?
Sentence (from "Zulema Castro de Peña"): Her two sons, Jesús Peña and Isidoro, disappeared during Dirty War of the 1970s, leading to her lifelong campaign for human rights and answers for the relatives of the "disappeared."
Relevant evidence: No