简述苯的中毒机制。
参考答案：
⑴干扰骨髓造血干细胞的生长和分化。
⑵氢醌与纺锤丝结合，抑制细胞增殖。
⑶损失DNA。
⑷激活癌基因。
The stranger stopped and turned around ___________to see is someone was following him.
A．every few meters
B．every a few meters
C．every other meters
D．every meters
肌沟法臂丛阻滞的缺点有哪些（）
A.尺神经阻滞不全或较迟
B.有损伤椎动脉的可能
C.有误入蛛网膜下隙和硬膜外下腔的危险
D.低位法可产生刺破胸膜产生气胸
E.不宜同时进行两侧阻滞
