Question: in which part of the u.s. is the majority of state boundaries based upon natural features
[{'answer': 'Midwest', 'provenance': [{'wikipedia_id': '1071969', 'title': 'List of river borders of U.S. states', 'start_paragraph_id': 1, 'start_character': 369, 'end_paragraph_id': 1, 'end_character': 376, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'North', 'provenance': [{'wikipedia_id': '1071969', 'title': 'List of river borders of U.S. states', 'start_paragraph_id': 1, 'start_character': 378, 'end_paragraph_id': 1, 'end_character': 383, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1071969', 'title': 'List of river borders of U.S. states', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 429, 'bleu_score': 0.970362113628587, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2723648100272281050}, 'section': 'Section::::Abstract.'}]}]