Question: in the pre-columbian era what were the only domesticated beasts of burden in the americas
[{'answer': 'alpacas', 'provenance': [{'wikipedia_id': '90001', 'title': 'Pre-Columbian era', 'start_paragraph_id': 95, 'start_character': 420, 'end_paragraph_id': 95, 'end_character': 427, 'bleu_score': 1.0, 'section': 'Section::::Agricultural development.\n'}]}, {'provenance': [{'wikipedia_id': '90001', 'title': 'Pre-Columbian era', 'start_paragraph_id': 95, 'start_character': 0, 'end_paragraph_id': 95, 'end_character': 663, 'bleu_score': 0.9813933169956551, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1369021946687563447}, 'section': 'Section::::Agricultural development.\n'}]}]