Question: what kind of joint is the si joint
[{'answer': 'a synovial plane joint', 'provenance': [{'wikipedia_id': '884723', 'title': 'Sacroiliac joint', 'start_paragraph_id': 1, 'start_character': 314, 'end_paragraph_id': 1, 'end_character': 336, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '884723', 'title': 'Sacroiliac joint', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 576, 'bleu_score': 0.9806740509884301, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16128308756331147091}, 'section': 'Section::::Abstract.'}]}]