Question: the ceasar salad was first served in which country
[{'answer': 'Mexico', 'provenance': [{'wikipedia_id': '6880', 'title': 'Caesar salad', 'start_paragraph_id': 4, 'start_character': 126, 'end_paragraph_id': 4, 'end_character': 132, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}]