Question: who won the us open tennis women's singles championship in 2013
[{'answer': 'Serena Williams', 'provenance': [{'wikipedia_id': '38458341', 'title': "2013 US Open – Women's Singles", 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 15, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '38458341', 'title': "2013 US Open – Women's Singles", 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 303, 'bleu_score': 0.6388458046698431, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6096828462255793440}, 'section': 'Section::::Abstract.'}]}]