Question: when did the musical mama mia come out
[{'answer': 'April 6 , 1999', 'provenance': [{'wikipedia_id': '252540', 'title': 'Mamma Mia!', 'start_paragraph_id': 10, 'start_character': 67, 'end_paragraph_id': 10, 'end_character': 81, 'bleu_score': 1.0, 'section': 'Section::::Productions.:Original West End production.\n'}]}]