心房颤动f波的频率为()
A.300~600/min
B.250~350/min
C.350~600/min
D.100~160/min
E.250~600/min
参考答案:C
简述AutoCAD中复制对象几种方式及命令。
You should________your spare time better if you want to be promoted.[ ]
A. take
B. employ
C. cost
D. improve