Question: who is the most successful goal scorer in the history of the eufa champions league
[{'answer': 'Cristiano Ronaldo', 'provenance': [{'wikipedia_id': '2947773', 'title': 'European Cup and UEFA Champions League records and statistics', 'start_paragraph_id': 637, 'start_character': 12, 'end_paragraph_id': 637, 'end_character': 29, 'bleu_score': 1.0, 'section': 'Section::::Players.:Goalscoring.:Top scorers by seasons.\n'}]}]