Question: when did work on the transcontinental railroad begin
[{'answer': '1863', 'provenance': [{'wikipedia_id': '36541', 'title': 'First Transcontinental Railroad', 'start_paragraph_id': 1, 'start_character': 166, 'end_paragraph_id': 1, 'end_character': 170, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '36541', 'title': 'First Transcontinental Railroad', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 942, 'bleu_score': 0.7603690193585511, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7716854151804997895}, 'section': 'Section::::Abstract.'}]}]