Which statement is true concerning dropping a pluggable database (PDB)?（）

• A、The PDB must be open in read-only mode.
• B、The PDB must be in mount state.
• C、The PDB must be unplugged.
• D、The PDB data files are always removed from disk.
• E、A dropped PDB can never be plugged back into a multitenant container database (CDB).