Explanation/Reference:
Explanation:
E: You can perform all ALTER PLUGGABLE DATABASE tasks by connecting to a PDB and running the corresponding ALTER DATABASE statement. This functionality is provided to maintain backward compatibility for applications that have been migrated to a CDB environment.
AG: When you issue an ALTER PLUGGABLE DATABASE OPEN statement, READ WRITE is the default unless a PDB being opened belongs to a CDB that is used as a physical standby database, in which case READ ONLY is the default.
You can specify which PDBs to modify in the following ways:
List one or more PDBs.
Specify ALL to modify all of the PDBs.
Specify ALL EXCEPT to modify all of the PDBs, except for the PDBs listed.