电源机柜输出至基站主设备的电压（）.
A.-53V
B.53V
C.-48V
D.48V
参考答案：C
The speech that Mr.Smith made today gave a strong ______ on the students.
A．expression
B．expectation
C．reputation
D．impression
造成硫酸浓度倍差样的设备原因有管路阀门漏、仪表系统故障、管路不畅。
