Question: who won the 2018 mens us open tennis
[{'answer': 'Novak Djokovic', 'provenance': [{'wikipedia_id': '55901892', 'title': "2018 US Open – Men's Singles", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 14, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '55901892', 'title': "2018 US Open – Men's Singles", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 154, 'bleu_score': 0.767835058299373, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2182196473829880300}, 'section': 'Section::::Abstract.'}]}]