男孩，7岁。右下后牙自发痛3天。检查：<img src="/Image1/bc/bc87c0bb9f9455564bc2933bfb366d9e.jpg" />大面积龋坏，探及髓腔，无感觉。叩诊感不适，Ⅰ°松动，颊侧有瘘管。X线示<img src="/Image1/b4/b42868764ce1c0549a10c3e0c50932d2.jpg" />根分歧大量低密度影，恒牙胚牙囊骨硬板消失。<img src="/Image1/55/55edf76a9d82f70c360e51aeb453cbee.jpg" />缺失<img src="/Image1/a8/a8e8084c3ebfc77eaf55867e83215961.jpg" />萌出2／3，沟深，曾做过窝沟封闭。初步处理后，间隙管理方法是（）<br>A:观察间隙<br>B:功能保持器<br>C:丝圈保持器<br>D:下颌舌弓保持器<br>E:关闭间隙