Question: what is the shortest legal length of a shotgun barrel
[{'answer': '18 inches', 'provenance': [{'wikipedia_id': '498597', 'title': 'Sawed-off shotgun', 'start_paragraph_id': 1, 'start_character': 209, 'end_paragraph_id': 1, 'end_character': 218, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '498597', 'title': 'Sawed-off shotgun', 'start_paragraph_id': 27, 'start_character': 0, 'end_paragraph_id': 27, 'end_character': 1073, 'bleu_score': 0.851215692734643, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16147304872978646058}, 'section': 'Section::::Legal restrictions.:United States.\n'}]}]