Question: who sang vocals on saturday in the park
[{'answer': 'Robert Lamm', 'provenance': [{'wikipedia_id': '6377969', 'title': 'Saturday in the Park (song)', 'start_paragraph_id': 1, 'start_character': 44, 'end_paragraph_id': 1, 'end_character': 55, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Peter Cetera', 'provenance': [{'wikipedia_id': '6377969', 'title': 'Saturday in the Park (song)', 'start_paragraph_id': 9, 'start_character': 12, 'end_paragraph_id': 9, 'end_character': 24, 'bleu_score': 1.0, 'section': 'Section::::Personnel.\n'}]}]