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 "Mothers of the Plaza de Mayo"): The Mothers of the Plaza de Mayo (Spanish: "Asociación Madres de Plaza de Mayo" ) is an association of Argentine mothers whose children "disappeared" during the state terrorism of the military dictatorship, between 1976 and 1983.
Relevant evidence: Yes