Question: when does the 2017 regular season nfl start
[{'answer': 'September 7 , 2017', 'provenance': [{'wikipedia_id': '44726936', 'title': '2017 NFL season', 'start_paragraph_id': 1, 'start_character': 114, 'end_paragraph_id': 1, 'end_character': 132, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]