Question: who won back to back home run derbys
[{'answer': 'Ken Griffey Jr.', 'provenance': [{'wikipedia_id': '813519', 'title': 'Home Run Derby', 'start_paragraph_id': 31, 'start_character': 97, 'end_paragraph_id': 31, 'end_character': 112, 'bleu_score': 1.0, 'section': 'Section::::Television and radio coverage.\n'}]}, {'answer': 'Yoenis Céspedes', 'provenance': [{'wikipedia_id': '813519', 'title': 'Home Run Derby', 'start_paragraph_id': 7, 'start_character': 506, 'end_paragraph_id': 7, 'end_character': 521, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}]