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

[answerhappygod]

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)