Question: when was the north american free trade agreement signed
[{'answer': 'December 17 , 1992', 'provenance': [{'wikipedia_id': '22050', 'title': 'North American Free Trade Agreement', 'start_paragraph_id': 7, 'start_character': 141, 'end_paragraph_id': 7, 'end_character': 159, 'bleu_score': 1.0, 'section': 'Section::::Negotiation, ratification, and revision (1988–94).\n'}]}, {'provenance': [{'wikipedia_id': '22050', 'title': 'North American Free Trade Agreement', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 260, 'bleu_score': 0.520959792832522, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14825291059656708144}, 'section': 'Section::::Negotiation, ratification, and revision (1988–94).\n'}]}]