Creating Oracle Multitenant Databases - OCP: Oracle Database 12c Administrator Certified Professional - page 549

20. To drop a pluggable database, what steps are required? (Choose all that apply.)
A. The PDB must have been opened at least once.
B. You must specify an INTO clause and a valid XML target file.
C. The PDB must be closed.
D. The PDB must be in read-only mode.
E. None of the above.