Question: who was the first african american presidential candidate nominated
[{'answer': 'Frederick Douglass', 'provenance': [{'wikipedia_id': '21291394', 'title': 'African-American candidates for President of the United States', 'start_paragraph_id': 4, 'start_character': 11, 'end_paragraph_id': 4, 'end_character': 29, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '21291394', 'title': 'African-American candidates for President of the United States', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 487, 'bleu_score': 0.940033794885305, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4737730108183081312}, 'section': 'Section::::History.:Frederick Douglass.\n'}]}]