Question: when did the chicago bears start playing at soldier field
[{'answer': '1971', 'provenance': [{'wikipedia_id': '509225', 'title': 'Soldier Field', 'start_paragraph_id': 1, 'start_character': 218, 'end_paragraph_id': 1, 'end_character': 222, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '509225', 'title': 'Soldier Field', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 222, 'bleu_score': 0.950578622812921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13091499053362812986}, 'section': 'Section::::Abstract.'}]}]