静注吗啡后,呼吸抑制最明显的时间是在注射后()
A.1~2min
B.3~7min
C.8~10min
D.11~15min
E.16~20min
参考答案:B
The windows are _____________ the bed. [ ]
A. in
B. near
C. under
为什么等速送丝式自动焊机改变焊丝的送丝速度就可以改变焊接电流?