多通道协议包含一个控制通道和若干其它控制或数据通道，即控制信息的交互和数据的传送是在不同的通道上完成的，例如FTP和HTTP。（）
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最早的标注语言是（）
A. XML
B. HTML
C. VRML
D. SGML
You have enabled backup optimization in RMAN. You issue the following RMAN command to configure a redundancy-based retention policy： CONFIGURE RETENTION POLICY TO REDUNDANCY 3； Which statement is true？（）
A. The command fails because you cannot configure a redundancy-based retention policy when backup optimization is enabled
Backup optimization is performed， but RMAN considers the redundancy-based retention policy when it determines which datafiles should be backed up
C. Backup optimization is permanently disabled
D. Backup optimization is temporarily disabled because a redundancy-based retention policy is specified
烃类氧化产物包括（）。
A. 液体
B. 气体
C. 沉淀物
D. 以上三类都有
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