患儿女性，5岁，右肘部浅表瘢痕畸形，肘窝上、下各安放扩张器1个，规律注入0.9%氯化钠溶液1个月余，近1周出现右手背麻木，不能抬腕。

预防此类情况的关键是（）

A.减慢注液速度

B.抬高患肢

C.妥善安放扩张囊

D.加强关节锻炼

E.选择适当形状扩张器

I had to tell you that _____you do well in every subject, you won't be elected the monitor. [ ]

A. unless

B. if

C. because

D. when