Question: who won the men's us open 2017
[{'answer': 'Rafael Nadal', 'provenance': [{'wikipedia_id': '54523641', 'title': "2017 US Open – Men's Singles", 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 12, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '54523641', 'title': "2017 US Open – Men's Singles", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 519, 'bleu_score': 0.7195644929042431, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10563775741526080394}, 'section': 'Section::::Abstract.'}]}]