Question: who won the us open mens single title 2017
[{'answer': 'Rafael Nadal', 'provenance': [{'wikipedia_id': '51884449', 'title': '2017 US Open (tennis)', 'start_paragraph_id': 3, 'start_character': 44, 'end_paragraph_id': 3, 'end_character': 56, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '51884449', 'title': '2017 US Open (tennis)', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 199, 'bleu_score': 0.9364250605898111, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1757708917879448106}, 'section': 'Section::::Abstract.'}]}]