Question: when was the last time the arenal volcano erupted
[{'answer': 'May 7 , 1998', 'provenance': [{'wikipedia_id': '390861', 'title': 'Arenal Volcano', 'start_paragraph_id': 30, 'start_character': 17, 'end_paragraph_id': 30, 'end_character': 36, 'bleu_score': 1.0, 'section': 'Section::::Geologic history.:May 7, 1998.\n'}]}, {'provenance': [{'wikipedia_id': '390861', 'title': 'Arenal Volcano', 'start_paragraph_id': 30, 'start_character': 0, 'end_paragraph_id': 30, 'end_character': 289, 'bleu_score': 0.9645876452711911, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11115424101960696015}, 'section': 'Section::::Geologic history.:May 7, 1998.\n'}]}]