Question: who took over the mormon leadership and began the westward trek
[{'answer': 'Brigham Young', 'provenance': [{'wikipedia_id': '845910', 'title': 'Mormon pioneers', 'start_paragraph_id': 5, 'start_character': 41, 'end_paragraph_id': 5, 'end_character': 54, 'bleu_score': 1.0, 'section': 'Section::::Background of the migration.\n'}]}, {'provenance': [{'wikipedia_id': '845910', 'title': 'Mormon pioneers', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 1186, 'bleu_score': 0.9571831860741081, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7907005741893363231}, 'section': 'Section::::Background of the migration.\n'}]}]