Question: who played keyboard on the beatles rooftop concert
[{'answer': 'Billy Preston', 'provenance': [{'wikipedia_id': '41344149', 'title': "The Beatles' rooftop concert", 'start_paragraph_id': 1, 'start_character': 147, 'end_paragraph_id': 1, 'end_character': 160, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]