Question: when do the knockout stages of the champions league start
[{'answer': '13 February', 'provenance': [{'wikipedia_id': '54326297', 'title': '2017–18 UEFA Champions League knockout phase', 'start_paragraph_id': 1, 'start_character': 58, 'end_paragraph_id': 1, 'end_character': 69, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '54326297', 'title': '2017–18 UEFA Champions League knockout phase', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 271, 'bleu_score': 0.6650298392461971, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17714840040822877077}, 'section': 'Section::::Abstract.'}]}]