Question: what was the last horse to win triple crown
[{'answer': 'American Pharoah', 'provenance': [{'wikipedia_id': '19116721', 'title': 'Triple Crown of Thoroughbred Racing (United States)', 'start_paragraph_id': 3, 'start_character': 274, 'end_paragraph_id': 3, 'end_character': 290, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '19116721', 'title': 'Triple Crown of Thoroughbred Racing (United States)', 'start_paragraph_id': 3, 'start_character': 18, 'end_paragraph_id': 3, 'end_character': 302, 'bleu_score': 0.75640994636311, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13544593577706906286}, 'section': 'Section::::Abstract.'}]}]