Question: what is the oldest subway system in the us
[{'answer': 'Tremont Street Subway', 'provenance': [{'wikipedia_id': '2877372', 'title': 'Tremont Street subway', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 21, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2877372', 'title': 'Tremont Street subway', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 547, 'bleu_score': 0.951749605621204, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3617655517115392296}, 'section': 'Section::::Abstract.'}]}]