Question: when was sony walkman first sold in stores
[{'answer': 'the US in June 1980', 'provenance': [{'wikipedia_id': '29681566', 'title': 'Million Dollar Money Drop', 'start_paragraph_id': 20, 'start_character': 468, 'end_paragraph_id': 20, 'end_character': 487, 'bleu_score': 1.0, 'section': 'Section::::Controversies.\n'}]}, {'provenance': [{'wikipedia_id': '29681566', 'title': 'Million Dollar Money Drop', 'start_paragraph_id': 20, 'start_character': 0, 'end_paragraph_id': 20, 'end_character': 487, 'bleu_score': 0.8787011786519421, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9081069965741778847}, 'section': 'Section::::Controversies.\n'}]}]