Question: mid-ocean ridges form at which type of boundary
[{'answer': 'divergent plate boundary', 'provenance': [{'wikipedia_id': '1821971', 'title': 'Mid-ocean ridge', 'start_paragraph_id': 1, 'start_character': 248, 'end_paragraph_id': 1, 'end_character': 272, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]