Question: when did the brewers join the national league
[{'answer': '1998', 'provenance': [{'wikipedia_id': '13051421', 'title': '1998 Milwaukee Brewers season', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 4, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]