Question: where do tornadoes most commonly occur in the us
[{'answer': 'east of the Rocky Mountains', 'provenance': [{'wikipedia_id': '18436515', 'title': 'Tornadoes in the United States', 'start_paragraph_id': 2, 'start_character': 42, 'end_paragraph_id': 2, 'end_character': 69, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '18436515', 'title': 'Tornadoes in the United States', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 879, 'bleu_score': 0.967405819735595, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13081633230793601071}, 'section': 'Section::::Abstract.'}]}]