Question: when did the first episode of this is us air
[{'answer': 'September 20 , 2016', 'provenance': [{'wikipedia_id': '50526957', 'title': 'This Is Us (TV series)', 'start_paragraph_id': 1, 'start_character': 127, 'end_paragraph_id': 1, 'end_character': 146, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]