Question: when do you find out who a is season 1
[{'answer': 'March 21 , 2011', 'provenance': [{'wikipedia_id': '27047554', 'title': 'Pretty Little Liars (season 1)', 'start_paragraph_id': 1, 'start_character': 139, 'end_paragraph_id': 1, 'end_character': 156, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]