Question: when are the champions league semi finals played
[{'answer': '13 April 2018', 'provenance': [{'wikipedia_id': '54326297', 'title': '2017–18 UEFA Champions League knockout phase', 'start_paragraph_id': 42, 'start_character': 41, 'end_paragraph_id': 42, 'end_character': 54, 'bleu_score': 1.0, 'section': 'Section::::Semi-finals.\n'}]}]