You execute the following command to perform a backup by using Recovery Manager （RMAN）： RMAN> run {allocate channel c1 type sbt backup datafile 1 } The command errors out. A part of the error message is as follows： RMAN03009： failure of allocate command on c1 channel ORA19554： error allocating device， device type： SBT_TAPE， device name： What could explain why the statement failed？（）A.sbt is not a valid device type.B.Media Management Library was not loaded.C.The sbt device cannot be used for data file backups.D.No path was defined in the ALLOCATE CHANNEL command.E.The channel is currently being used by another RMAN session.

单项选择题

You execute the following command to perform a backup by using Recovery Manager （RMAN）： RMAN> run
{allocate channel c1 type sbt;
backup datafile 1;
}
The command errors out. A part of the error message is as follows：
RMAN03009： failure of allocate command on c1 channel
ORA19554： error allocating device， device type： SBT_TAPE， device name：
What could explain why the statement failed？（）

A.sbt is not a valid device type.
B.Media Management Library was not loaded.
C.The sbt device cannot be used for data file backups.
D.No path was defined in the ALLOCATE CHANNEL command.
E.The channel is currently being used by another RMAN session.

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