Question: when did mcdonald's start selling happy meals
[{'answer': 'June 1979', 'provenance': [{'wikipedia_id': '484398', 'title': 'Happy Meal', 'start_paragraph_id': 1, 'start_character': 104, 'end_paragraph_id': 1, 'end_character': 113, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '484398', 'title': 'Happy Meal', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 369, 'bleu_score': 0.7714294633673281, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1617495511346305004}, 'section': 'Section::::Abstract.'}]}]