Question: when do the majority of tornadoes occur in north america
[{'answer': 'March through June', 'provenance': [{'wikipedia_id': '18436515', 'title': 'Tornadoes in the United States', 'start_paragraph_id': 4, 'start_character': 73, 'end_paragraph_id': 4, 'end_character': 91, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '18436515', 'title': 'Tornadoes in the United States', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 603, 'bleu_score': 0.955468993395951, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11753963546757363615}, 'section': 'Section::::Abstract.'}]}]