Question: when did the mormon pioneers cross the plains
[{'answer': 'April 1847', 'provenance': [{'wikipedia_id': '845910', 'title': 'Mormon pioneers', 'start_paragraph_id': 2, 'start_character': 448, 'end_paragraph_id': 2, 'end_character': 458, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '845910', 'title': 'Mormon pioneers', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 932, 'bleu_score': 0.9626201417602621, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11654288154942673940}, 'section': 'Section::::Abstract.'}]}]