Question: how many simpsons treehouse of horrors episodes are there
[{'answer': 'twenty - seven'}, {'provenance': [{'wikipedia_id': '14104750', 'title': 'List of The Simpsons Treehouse of Horror episodes', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 495, 'bleu_score': 0.9132932539604991, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2117087206837945380}, 'section': 'Section::::Abstract.'}]}]