What rivers were located next to ancient Sumer?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'INTERNAL', 'name_': 'Q11767', 'id': 0, 'label': 'Mesopotamia'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q35355', 'id': 1, 'label': 'Sumer'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q34589', 'id': 2, 'label': 'Euphrates'}, {'type': 'INTERNAL', 'name_': 'Q22815091', 'id': 3, 'label': 'The Sawley Map'}], 'links': [{'name_': 'P361', 'source': 1, 'target': 0, 'label': 'part of'}, {'name_': 'P180', 'source': 3, 'target': 0, 'label': 'depicts'}, {'name_': 'P180', 'source': 3, 'target': 2, 'label': 'depicts'}]}