Question: when did bert and ernie first appear on sesame street
[{'answer': 'July 1969', 'provenance': [{'wikipedia_id': '42965384', 'title': 'Bert and Ernie', 'start_paragraph_id': 5, 'start_character': 178, 'end_paragraph_id': 5, 'end_character': 187, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '42965384', 'title': 'Bert and Ernie', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 437, 'bleu_score': 0.97451705556073, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12716075370047074921}, 'section': 'Section::::History.\n'}]}]