Question: where does mexico city rank among the world's largest cities
[{'answer': 'tenth - largest agglomeration'}, {'provenance': [{'wikipedia_id': '18987', 'title': 'Mexico City', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 411, 'bleu_score': 0.6663668862569131, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8200270471284407833}, 'section': 'Section::::Abstract.'}]}]