Question: when does the challenge champs vs stars start
[{'answer': 'November 21 , 2017', 'provenance': [{'wikipedia_id': '1475688', 'title': 'The Challenge (TV series)', 'start_paragraph_id': 53, 'start_character': 128, 'end_paragraph_id': 53, 'end_character': 146, 'bleu_score': 1.0, 'section': 'Section::::Specials.:"The Challenge: Champs vs. Stars".:"The Challenge: Champs vs. Stars" (season 2).\n'}]}]