Question: when did the pittsburgh steelers join the nfl
[{'answer': 'July 8 , 1933', 'provenance': [{'wikipedia_id': '23338', 'title': 'Pittsburgh Steelers', 'start_paragraph_id': 3, 'start_character': 143, 'end_paragraph_id': 3, 'end_character': 156, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '23338', 'title': 'Pittsburgh Steelers', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 1170, 'bleu_score': 0.9900246259093721, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12759508856292385081}, 'section': 'Section::::Abstract.'}]}]