Question: when did the beatles first play the cavern
[{'answer': '21 February 1957', 'provenance': [{'wikipedia_id': '22813000', 'title': 'The Beatles at The Cavern Club', 'start_paragraph_id': 2, 'start_character': 227, 'end_paragraph_id': 2, 'end_character': 243, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '22813000', 'title': 'The Beatles at The Cavern Club', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 762, 'bleu_score': 0.959893969644335, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1880504639173147067}, 'section': 'Section::::Abstract.'}]}]