函数在x处的微分为()。
A.
B.
C.xdx
D.
参考答案:A
This is a nice city ______ many interesting places. [ ]
A. with
B. have
C. has
D. there are
一般机床操作( )应检查设备的防护、保险、信号装置是否完好。
A.前
B.后
C.中
D.卸下工件