单项选择题 Your multitenant container database, CDB1, is running in ARCHIVELOG mode and has two pluggable databases, HR_PDB and ACCOUNTS_PDB. An RMAN backup exists for the database. You issue the command to open ACCOUNTS_PDB and find that the USERDATA.DBF data file for the default permanent tablespace USERDATA belonging to ACCOUNTS_PDB is corrupted. What should you do before executing the commands to restore and recover the data file in ACCOUNTS_PDB?（）

多项选择题 You are administering a database stored in Automatic Storage Management (ASM). You use RMAN to back up the database and the MD_BACKUP command to back up the ASM metadata regularly. You lost an ASM disk group DG1 due to hardware failure. In which three ways can you re-create the lost disk group and restore the data?（）

单项选择题 Which statement is true about Oracle Net Listener?（）