Question: when did serena williams win her last grand slam
[{'answer': '2017', 'provenance': [{'wikipedia_id': '164910', 'title': 'Serena Williams', 'start_paragraph_id': 1, 'start_character': 231, 'end_paragraph_id': 1, 'end_character': 235, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]