子宫肌瘤（）

A.子宫超声显示子宫增大，子宫壁可见边缘清楚的实质性暗区，中间有稀疏光点

B.子宫超声显示子宫增大，其中光点增多了，可见圆形妊娠环

C.子宫超声显示子宫增大，子宫前后壁光带之间出现散在的光点密集，夹杂有大小不等的液性暗区呈飞雪状

D.子宫超声显示子宫增大，可见胎心搏动和胎动

E.子宫超声显示子宫增大胎儿双顶径为7.5cm

Which characteristic of Halon is a disadvantage when it is used as a fire extinguishing medium?（）

A.Leaves a residue

B.Cost，relative to other agents

C.Breaks down while under prolonged storage

D.Conducts electricity