Question: what were the two main causes of the dust bowl
[{'answer': 'severe drought', 'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', 'start_paragraph_id': 1, 'start_character': 154, 'end_paragraph_id': 1, 'end_character': 168, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'failure to apply dryland farming methods to prevent wind erosion'}, {'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 1006, 'bleu_score': 0.5666769387542301, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17306417650844211093}, 'section': 'Section::::Abstract.'}]}]