Question: elevation above which it is too cold for trees to grow
[{'answer': 'tree line', 'provenance': [{'wikipedia_id': '463469', 'title': 'Tree line', 'start_paragraph_id': 1, 'start_character': 4, 'end_paragraph_id': 1, 'end_character': 13, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '463469', 'title': 'Tree line', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 425, 'bleu_score': 0.7394990532647371, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17919917833770748515}, 'section': 'Section::::Abstract.'}]}]