Question: when does the final episode of once upon a time air
[{'answer': 'May 18 , 2018', 'provenance': [{'wikipedia_id': '54030079', 'title': 'Once Upon a Time (season 7)', 'start_paragraph_id': 3, 'start_character': 277, 'end_paragraph_id': 3, 'end_character': 290, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '54030079', 'title': 'Once Upon a Time (season 7)', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 289, 'bleu_score': 0.9298663600557571, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15614565715524628666}, 'section': 'Section::::Abstract.'}]}]