Question: when did simon and garfunkel perform in central park
[{'answer': 'September 1981', 'provenance': [{'wikipedia_id': '34953952', 'title': 'The Concert in Central Park', 'start_paragraph_id': 1, 'start_character': 168, 'end_paragraph_id': 1, 'end_character': 182, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '34953952', 'title': 'The Concert in Central Park', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 798, 'bleu_score': 0.5938057021469351, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16277912766342949154}, 'section': 'Section::::Abstract.'}]}]