Question: when did the mcguire sisters perform on pbs
[{'answer': '2004', 'provenance': [{'wikipedia_id': '588388', 'title': 'The McGuire Sisters', 'start_paragraph_id': 18, 'start_character': 638, 'end_paragraph_id': 18, 'end_character': 642, 'bleu_score': 1.0, 'section': "Section::::End to the group's public appearances.\n"}]}, {'provenance': [{'wikipedia_id': '588388', 'title': 'The McGuire Sisters', 'start_paragraph_id': 18, 'start_character': 0, 'end_paragraph_id': 18, 'end_character': 821, 'bleu_score': 0.985238839858627, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11163040450816005417}, 'section': "Section::::End to the group's public appearances.\n"}]}]