Question: who won the men's singles title of the us open tennis grand slam 2014
[{'answer': 'Marin Čilić', 'provenance': [{'wikipedia_id': '42936034', 'title': "2014 US Open – Men's Singles", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 11, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '42936034', 'title': "2014 US Open – Men's Singles", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 110, 'bleu_score': 0.8914703664390791, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15489273835300313004}, 'section': 'Section::::Abstract.'}]}]