You received these error messages because the client cannot find the desired database：  
ORA-12198： TNS：could not path to destination 
ORA-12203： TNS：unable to connect to destination 
Which action would be appropriate in helping to resolve the errors？（）

单项选择题Oracle Net Services is composed of several communication layers， known as a stack，which enables clients and database severs to share，modify，and manipulate data. Which reveals the correct architecture，in hierarchical order，of the client-side stack？（）

A.A
B.B
C.C
D.D

单项选择题WhichstatementistrueregardingRMANcomponents？（）

A.Each target database requires its own recover catalog. 
B.RMAN scripts can be stored in the recovery catalog or the target control file. 
C.A channel is a stream of data to a device type and corresponds to one server session. 
D.The RMAN executable interprets sever session commands and establishes connections to the target database.

单项选择题You issue this statement：ALTER DATABASE BACKUP CONTROLFILE TO TRACE；  What does the statement generate？（）

A.A text copy of the control file.
B.A binary copy of the control file.
C.A file containing a SQL statement which will re-create the database.
D.A file containing a SQL statement which will re-create the control file.

单项选择题Whichstatementistrueregardingcheckpointsandrecovery？（）

A.A checkpoint defines the highest system change number （SCN）.
B.All redo entries higher or at the SCN are known to be written to the data files.
C.Only the redo records containing SCNs higher then the checkpoint need to be applied during recovery.
D.The LOG_CHECKPOINT_INTERVAL initialization parameter specifies the amount of time between incremental checkpoints.

单项选择题Inuser-managedbackupandrecoverprocedures，howaredatafilesbackedup？（）

A.Using SQL commands.
B.Using SQL*Plus commands.
C.Using operating system commands.
D.Using Recover Manager commands.