Question: when was the first volvo truck introduced in the united states
[{'answer': '1980', 'provenance': [{'wikipedia_id': '40160680', 'title': 'Volvo Trucks', 'start_paragraph_id': 30, 'start_character': 458, 'end_paragraph_id': 30, 'end_character': 462, 'bleu_score': 1.0, 'section': 'Section::::Volvo Trucks worldwide.:North America.\n'}]}]