Question: nitrogenous wastes may be produced as a result of the metabolism of
[{'answer': 'protein', 'provenance': [{'wikipedia_id': '4482716', 'title': 'Metabolic waste', 'start_paragraph_id': 4, 'start_character': 228, 'end_paragraph_id': 4, 'end_character': 235, 'bleu_score': 1.0, 'section': 'Section::::Nitrogen wastes.\n'}]}, {'provenance': [{'wikipedia_id': '4482716', 'title': 'Metabolic waste', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 344, 'bleu_score': 0.918221068290973, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5747714972017242816}, 'section': 'Section::::Nitrogen wastes.\n'}]}]