Question: what type of glacier forms a u shaped valley
[{'answer': 'mountain glaciation', 'provenance': [{'wikipedia_id': '6194438', 'title': 'U-shaped valley', 'start_paragraph_id': 1, 'start_character': 121, 'end_paragraph_id': 1, 'end_character': 140, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6194438', 'title': 'U-shaped valley', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 611, 'bleu_score': 0.943950247594541, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10611434263280228498}, 'section': 'Section::::Abstract.'}]}]