Question: when did the broncos win back to back super bowls
[{'answer': '1997 ( XXXII )'}, {'answer': '1998 ( XXXIII )'}, {'provenance': [{'wikipedia_id': '8122', 'title': 'Denver Broncos', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 854, 'bleu_score': 0.757891696256304, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8114079331599186161}, 'section': 'Section::::Abstract.'}]}]