Question: when was the euro introduced as legal currency
[{'answer': '1 January 1999', 'provenance': [{'wikipedia_id': '8459263', 'title': 'History of the euro', 'start_paragraph_id': 1, 'start_character': 32, 'end_paragraph_id': 1, 'end_character': 46, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '8459263', 'title': 'History of the euro', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 448, 'bleu_score': 0.97451705556073, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 348651126851414587}, 'section': 'Section::::Abstract.'}]}]