What is the chief river of the second-largest drainage system on the North American continent that does not border Pennsylvania?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'INTERNAL', 'name_': 'Q1860', 'id': 0, 'label': 'English'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q781', 'id': 1, 'label': 'Antigua and Barbuda'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q49', 'id': 2, 'label': 'North America'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q1400', 'id': 3, 'label': 'Pennsylvania'}], 'links': [{'name_': 'P17', 'source': 0, 'target': 1, 'label': 'country'}, {'name_': 'P37', 'source': 1, 'target': 0, 'label': 'official language'}, {'name_': 'P17', 'source': 1, 'target': 1, 'label': 'country'}, {'name_': 'P30', 'source': 1, 'target': 2, 'label': 'continent'}, {'name_': 'P37', 'source': 3, 'target': 0, 'label': 'official language'}, {'name_': 'P30', 'source': 3, 'target': 2, 'label': 'continent'}]}