上卸冲管时要站稳,握牢榔头并(),避免砸伤腿脚和榔头脱落伤人。
A. 栓保险绳
B. 戴好手套
C. 接套管
D. 猛砸
储备浮力的大小通常以满载排水量的百分比来表示,海船一般为()。
A. 10%~15%
B. 25%~40%
C. 50%~60%
D. 20%~50%
在采用比例调节器的控制系统中,被控量变化全量程的一半,调节阀开度变化全行程,调节器的PB为()。
A. PB=50%
B. PB=100%
C. PB=150%
D. PB=200%
The database is running in NOARCHIVELOG mode. A data file is lost. Which two are valid options for recover?()
A. Restore the data file and perform incomplete recovery.
B. Restore the data file and perform point-in-time recover.
C. Drop the tablespace and lose all data in the tablespace.
D. Restore the database and lose all data since the last backup.