Question: the initial stage of blood filtration in the kidneys occurs in which portion of the nephron
[{'answer': 'renal corpuscle', 'provenance': [{'wikipedia_id': '17025', 'title': 'Kidney', 'start_paragraph_id': 11, 'start_character': 522, 'end_paragraph_id': 11, 'end_character': 537, 'bleu_score': 1.0, 'section': 'Section::::Structure.:Gross anatomy.\n'}]}, {'provenance': [{'wikipedia_id': '17025', 'title': 'Kidney', 'start_paragraph_id': 39, 'start_character': 0, 'end_paragraph_id': 39, 'end_character': 410, 'bleu_score': 0.859733271223698, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12507359429957729749}, 'section': 'Section::::Function.:Formation of urine.:Filtration.\n'}]}]