Question: when did the last steam train run on the london underground
[{'answer': '1961', 'provenance': [{'wikipedia_id': '38861956', 'title': 'Metropolitan Railway steam locomotives', 'start_paragraph_id': 7, 'start_character': 752, 'end_paragraph_id': 7, 'end_character': 756, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '38861956', 'title': 'Metropolitan Railway steam locomotives', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 756, 'bleu_score': 0.9839344367380701, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14576998468049838733}, 'section': 'Section::::History.\n'}]}]