Question: whom did the free-soil party nominate as its presidential candidate in 1848
[{'answer': 'Martin Van Buren', 'provenance': [{'wikipedia_id': '40515', 'title': '1848 United States presidential election', 'start_paragraph_id': 2, 'start_character': 548, 'end_paragraph_id': 2, 'end_character': 564, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '40515', 'title': '1848 United States presidential election', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 774, 'bleu_score': 0.9434284474672501, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 732932824808202362}, 'section': 'Section::::Abstract.'}]}]