Question: who has won back to back premier league titles
[{'answer': 'Manchester United', 'provenance': [{'wikipedia_id': '3548404', 'title': 'List of English football champions', 'start_paragraph_id': 4, 'start_character': 628, 'end_paragraph_id': 4, 'end_character': 645, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Chelsea', 'provenance': [{'wikipedia_id': '3548404', 'title': 'List of English football champions', 'start_paragraph_id': 4, 'start_character': 599, 'end_paragraph_id': 4, 'end_character': 606, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]