Who was the first black senator in the U.S.?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'QUESTIONS_ENTITY', 'name_': 'Q30', 'id': 0, 'label': 'United States of America'}, {'type': 'INTERNAL', 'name_': 'Q6219407', 'id': 1, 'label': 'John Armstrong'}, {'type': 'INTERNAL', 'name_': 'Q20824348', 'id': 2, 'label': 'American National Biography Online'}, {'type': 'INTERNAL', 'name_': 'Q103876774', 'id': 3, 'label': 'Revels, Hiram Rhoades (27 September 1827?–16 January 1901), senator, clergyman, and educator'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q719200', 'id': 4, 'label': 'Hiram Rhodes Revels'}], 'links': [{'name_': 'P17', 'source': 0, 'target': 0, 'label': 'country'}, {'name_': 'P27', 'source': 1, 'target': 0, 'label': 'country of citizenship'}, {'name_': 'P1343', 'source': 1, 'target': 2, 'label': 'described by source'}, {'name_': 'P1433', 'source': 3, 'target': 2, 'label': 'published in'}, {'name_': 'P921', 'source': 3, 'target': 4, 'label': 'main subject'}]}