Question: when did grant take charge of the union army
[{'answer': '1864', 'provenance': [{'wikipedia_id': '30098820', 'title': 'Ulysses S. Grant and the American Civil War', 'start_paragraph_id': 2, 'start_character': 518, 'end_paragraph_id': 2, 'end_character': 522, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '30098820', 'title': 'Ulysses S. Grant and the American Civil War', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 935, 'bleu_score': 0.9874601949752461, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6993675401730650958}, 'section': 'Section::::Abstract.'}]}]