Zulema Castro de Peña was a member of what organization that began to march in 1977 at the Plaza de Mayo in Buenos Aires?
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. Mothers of the Plaza de Mayo:  They organized while trying to learn what had happened to their children, and began to march in 1977 at the Plaza de Mayo in Buenos Aires, in front of the Casa Rosada presidential palace, in public defiance of the government's state terrorism intended to silence all opposition.
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