Which two are true about gathering optimizer statistics? (Choose two.) 

Answer options:

A. Executing DBMS_STATS.GATHER_DATABASE_STATS while connected to CDB$ROOT gathers object statistics in all open PDBs except PDB$SEED.B. Executing DBMS_STATS.GATHER_DATABASE_STATS while connected to a PDB opened in read/write mode gathers object statistics for that PDB.C. Executing DBMS_STATS.GATHER_DATABASE_STATS while connected to CDB$ROOT gathers object statistics only in CDB$ROOT.
D. System statistics can be gathered only while connected to CDB$ROOT.
E. Executing DBMS_STATS.GATHER_DATABASE_STATS while connected to CDB$ROOT gathers object statistics in all open pluggable databases (PDBs)

CE

Reference: https://docs.oracle.com/en/database/oracle/oracle-database/20/arpls/DBMS_STATS.html