A (not B,not E): The CREATE DATABASE ...ENABLE PLUGGABLE DATABASE SQL
statement creates a new CDB. If you do not specify the ENABLE PLUGGABLE
DATABASE clause, then the newly created database is a non-CDB and can never contain
PDBs.
D: You can create a PDB by plugging in a Non-CDB as a PDB.
Thefollowing graphic depicts the options for creating a PDB:

Incorrect:
Not E: For the duration of its existence, a database is either a CDB or a non-CDB. You cannot transform a non-CDB into a CDB or vice versa. You must define a database as a
CDB at creation, and then create PDBs within this CDB.

Explanation/Reference:
Explanation:
https://logicalread.com/oracle-latch-free-wait-dr01/#.WQygk1i6zUI

Explanation
References: https://docs.oracle.com/cd/B19306_01/server.102/b14215/ldr_modes.htm#i1007501

utlrp.sql and utlprp.sql
The utlrp.sql and utlprp.sql scripts are provided by Oracle to recompile all invalid objects in the
database. They are typically run after major database changes such as upgrades or patches. They
are located in the $ORACLE_HOME/rdbms/admin directory and provide a wrapper on the
UTL_RECOMP package. The utlrp.sql script simply calls the utlprp.sql script with a command line
parameter of "0". The utlprp.sql accepts a single integer parameter that indicates the level of
parallelism as follows.
0 - The level of parallelism is derived based on the CPU_COUNT parameter.
1 - The recompilation is run serially, one object at a time.
N - The recompilation is run in parallel with "N" number of threads.
Both scripts must be run as the SYS user, or another user with SYSDBA, to work correctly.
Reference: Recompiling Invalid Schema Objects