Question: when did the washington nationals become a baseball team
[{'answer': '1969', 'provenance': [{'wikipedia_id': '885151', 'title': 'Washington Nationals', 'start_paragraph_id': 2, 'start_character': 159, 'end_paragraph_id': 2, 'end_character': 163, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]