Question: how many dukes of edinburgh have there been
[{'answer': 'four'}, {'provenance': [{'wikipedia_id': '153927', 'title': 'Duke of Edinburgh', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 239, 'bleu_score': 0.7466745587002921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13139751036889495512}, 'section': 'Section::::Abstract.'}]}]