Question: what type of cells are white blood cells
[{'answer': 'cells of the immune system', 'provenance': [{'wikipedia_id': '25164668', 'title': 'White blood cell', 'start_paragraph_id': 1, 'start_character': 89, 'end_paragraph_id': 1, 'end_character': 115, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '25164668', 'title': 'White blood cell', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 417, 'bleu_score': 0.9694566079002921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17213283719650764404}, 'section': 'Section::::Abstract.'}]}]