We must take two aspects into consideration, both of __________ associated with the safety of the students .

A．which

B．whom

C．that

D．them

男性，49岁。左下拔牙区阵发性酸痛4年。4年前有左下牙拔除史。口内检查见：左下第1磨牙缺失，牙龈表现正常，无隆起性改变。左下颌骨侧位片显示：坐下颌第1磨牙缺失，其牙槽部有直径为1cm的类圆形骨质密度降低区，边缘光滑。考虑（）

A.左下颌骨残余囊肿

B.左下颌骨根尖周囊肿

C.左下颌骨根尖囊肿

D.左下颌骨牙囊肿

E.左下颌骨根尖骨坏死