Question: how many times has serena and venus played each other
[{'answer': '29'}, {'provenance': [{'wikipedia_id': '21800697', 'title': 'Williams sisters rivalry', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 269, 'bleu_score': 0.7442217013596201, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7383144854057045185}, 'section': 'Section::::Abstract.'}]}]