Question: a rift valley is evidence of which kind of plate boundary
[{'answer': 'a divergent plate boundary', 'provenance': [{'wikipedia_id': '497007', 'title': 'Rift valley', 'start_paragraph_id': 1, 'start_character': 164, 'end_paragraph_id': 1, 'end_character': 190, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '497007', 'title': 'Rift valley', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 1152, 'bleu_score': 0.9391392137735721, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4794310802309332770}, 'section': 'Section::::Abstract.'}]}]