Which two are true about gathering optimizer statistics? (Choose two.)
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)正确答案BC
