Question: when did unions start in the united states
[{'answer': 'mid-19th century', 'provenance': [{'wikipedia_id': '2474406', 'title': 'Labor unions in the United States', 'start_paragraph_id': 7, 'start_character': 28, 'end_paragraph_id': 7, 'end_character': 44, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '2474406', 'title': 'Labor unions in the United States', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 409, 'bleu_score': 0.930807147807393, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16051231386933968654}, 'section': 'Section::::History.\n'}]}]