Question: when did iowa become a right to work state
[{'answer': '1947', 'provenance': [{'wikipedia_id': '392198', 'title': 'Right-to-work law', 'start_paragraph_id': 3, 'start_character': 318, 'end_paragraph_id': 3, 'end_character': 322, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]