Which three statements are true about the stages of database startup?
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Data files and redo log files can be renamed at the MOUNT stage.
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Control files are required to bring the database to the NOMOUNT stage.
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Data files and online redo log files are checked for consistency while opening the database.
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Data files and redo log files are made available to users at the OPEN stage.
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Control files are read at the OPEN stage for the location of data files.
At NOMOUNT stage, Oracle reads the parameter file to locate control files but control files themselves are required. At MOUNT stage, control files are read and data files/redo logs can be renamed using ALTER DATABASE commands. At OPEN stage, Oracle checks file consistency and makes data accessible to users. Control files are read at MOUNT stage, not OPEN stage. The consistency check happens during MOUNT, not OPEN.
At the MOUNT stage the database has associated its control file(s) but not yet opened datafiles, which is exactly when datafiles and redo logs can be renamed since Oracle only needs the control file to track them at that point. Control files must be present just to reach NOMOUNT→MOUNT, and only at the OPEN stage are datafiles and online redo logs actually made available to users for reads/writes; consistency checking and reading datafile locations from the control file happen during the mount phase, not while opening.