Who is the lead singer of Black Sabbath?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q1133657', 'id': 0, 'label': 'traditional heavy metal'}, {'type': 'INTERNAL', 'name_': 'Q838908', 'id': 1, 'label': 'Mob Rules'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q47670', 'id': 2, 'label': 'Black Sabbath'}], 'links': [{'name_': 'P136', 'source': 1, 'target': 0, 'label': 'genre'}, {'name_': 'P175', 'source': 1, 'target': 2, 'label': 'performer'}]}