Question: according to the preamble what was the main concern of the knights of labor
[{'answer': 'eight - hour day', 'provenance': [{'wikipedia_id': '17387', 'title': 'Knights of Labor', 'start_paragraph_id': 1, 'start_character': 458, 'end_paragraph_id': 1, 'end_character': 473, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '17387', 'title': 'Knights of Labor', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 473, 'bleu_score': 0.7322139645214251, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6837639892752845120}, 'section': 'Section::::Origins.\n'}]}]