Question: what was the chief city of the aztec civilization
[{'answer': 'Tenochtitlan', 'provenance': [{'wikipedia_id': '4885862', 'title': 'History of the Aztecs', 'start_paragraph_id': 2, 'start_character': 36, 'end_paragraph_id': 2, 'end_character': 48, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4885862', 'title': 'History of the Aztecs', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 436, 'bleu_score': 0.8103022252481481, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7988559223407777742}, 'section': 'Section::::Abstract.'}]}]