Question: when did coal become a major energy source
[{'answer': 'the Industrial Revolution', 'provenance': [{'wikipedia_id': '1454146', 'title': 'History of coal mining', 'start_paragraph_id': 1, 'start_character': 80, 'end_paragraph_id': 1, 'end_character': 105, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1454146', 'title': 'History of coal mining', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 1354, 'bleu_score': 0.9908043535876511, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16348529148562277694}, 'section': 'Section::::Abstract.'}]}]