Question: on which date south africa become a democratic republic
[{'answer': '31 May 1961', 'provenance': [{'wikipedia_id': '1931950', 'title': '1960 South African republic referendum', 'start_paragraph_id': 1, 'start_character': 562, 'end_paragraph_id': 1, 'end_character': 573, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1931950', 'title': '1960 South African republic referendum', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 573, 'bleu_score': 0.9792717993254391, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 908880572397695349}, 'section': 'Section::::Abstract.'}]}]