Question: when was the sony walkman sold in stores
[{'answer': 'June 1980', 'provenance': [{'wikipedia_id': '29681566', 'title': 'Million Dollar Money Drop', 'start_paragraph_id': 20, 'start_character': 478, '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': 13801454573139904629}, 'section': 'Section::::Controversies.\n'}]}]