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"): Zulema Castro de Peña (c. 1920 – January 22, 2013) was an Argentine human rights activist and member of the Mothers of the Plaza de Mayo.
Relevant evidence: Yes