Question: when does nathan find out about chuck and blair
[{'answer': '13th episode', 'provenance': [{'wikipedia_id': '15173075', 'title': 'The Thin Line Between Chuck and Nate', 'start_paragraph_id': 1, 'start_character': 46, 'end_paragraph_id': 1, 'end_character': 58, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '15173075', 'title': 'The Thin Line Between Chuck and Nate', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 242, 'bleu_score': 0.9529077664391161, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16909840057553853462}, 'section': 'Section::::Abstract.'}]}]