Question: when does season 4 of agents of shield start
[{'answer': 'September 20 , 2016', 'provenance': [{'wikipedia_id': '49635999', 'title': 'Agents of S.H.I.E.L.D. (season 4)', 'start_paragraph_id': 73, 'start_character': 55, 'end_paragraph_id': 73, 'end_character': 74, 'bleu_score': 1.0, 'section': 'Section::::Release.:Broadcast.\n'}]}]