Question: when was the hoover dam built and finished
[{'answer': 'between 1931 and 1936', 'provenance': [{'wikipedia_id': '14308', 'title': 'Hoover Dam', 'start_paragraph_id': 1, 'start_character': 165, 'end_paragraph_id': 1, 'end_character': 186, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '14308', 'title': 'Hoover Dam', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 561, 'bleu_score': 0.9788329837059241, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6966238272934821551}, 'section': 'Section::::Abstract.'}]}]