Your database instance is running with full workload after database creation. You have decided to use a fixed-size undo tablespace. You want to use the Undo Advisor to estimate the capacity of the undo tablespace. Which two factors must you consider before using the Undo Advisor to estimate the capacity of the undotablespace（）

A. The retention period to support flashback
B. The expected length of the longest-running query
C. The number of undo tablespaces in the database
D. The size of the Flash Recovery Area for the database instance