起吊设备头部用的吊车，称为主吊吊车。设备尾部送尾吊车或称为辅助吊车。
查看答案
移动设备的转动部位允许有油迹，擦干后（）分钟不成滴。
系统中的签约依据一旦被某份合同引用后，就不可以再进行修改。
A. 正确
B. 错误
To clean up old records that are in a Flashback Data Archive and are past the retention period， what must the DBA do？（）
A. TRUNCATE the archive table.
B. DROP the Flashback Data Archive.
C. Nothing；expired rows are automatically removed.
D. Nothing；expired rows are moved to an archive table.
E. Delete entries from the archive where the metadata date retained is greater than the retention period.
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