Question: when did zebra mussels come to north america
[{'answer': '1988', 'provenance': [{'wikipedia_id': '488945', 'title': 'Zebra mussel', 'start_paragraph_id': 25, 'start_character': 57, 'end_paragraph_id': 25, 'end_character': 61, 'bleu_score': 1.0, 'section': 'Section::::As an invasive species.:North American invasion.\n'}]}, {'provenance': [{'wikipedia_id': '488945', 'title': 'Zebra mussel', 'start_paragraph_id': 25, 'start_character': 0, 'end_paragraph_id': 25, 'end_character': 847, 'bleu_score': 0.9858648355536391, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4786993914335582335}, 'section': 'Section::::As an invasive species.:North American invasion.\n'}]}]