Question: name the four us presidents who were assassinated while in office
[{'answer': 'Abraham Lincoln ( 1865 )', 'provenance': [{'wikipedia_id': '574536', 'title': 'List of United States presidential assassination attempts and plots', 'start_paragraph_id': 1, 'start_character': 337, 'end_paragraph_id': 1, 'end_character': 360, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'William McKinley ( 1901 )', 'provenance': [{'wikipedia_id': '574536', 'title': 'List of United States presidential assassination attempts and plots', 'start_paragraph_id': 1, 'start_character': 387, 'end_paragraph_id': 1, 'end_character': 411, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'John F. Kennedy ( 1963 )'}, {'answer': 'James A. Garfield ( 1881 )'}, {'provenance': [{'wikipedia_id': '574536', 'title': 'List of United States presidential assassination attempts and plots', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 612, 'bleu_score': 0.9792717993254391, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1468562846110755002}, 'section': 'Section::::Abstract.'}]}]