Explanation:
PGA_AGGREGATE_TARGET is a new instance-level parameter that specifies the total memory in KB, MB, or GB for the PGA of all the sessions combined. This is a dynamic parameter; you can set this parameter with the ALTER SYSTEM command. Oracle9i gives you a second parameter, WORKAREA_SIZE_POLICY, to specify the work-areasizing mechanism. This is also a dynamic parameter that you can set with the ALTER SYSTEM or ALTER SESSION commands.
Incorrect Answers:
1: To enable Automated SQL Execution Memory Management you don’t need to execute the DBMS_STATS.GATHER_SYSTEM_STATS procedure.
3: You cannot set the instance parameters SORT_ AREA_ SIZE, BITMAP_MERGE_AREA_SIZE, CREATE_BITMAP_AREA_SIZE, HASH_AREA_SIZE, SORT_AREA_SIZE, and SORT_AREA_RETAINED_SIZE all to AUTO value.
4: You cannot unset the instance parameters SORT_ AREA_ SIZE, BITMAP_MERGE_AREA_SIZE, CREATE_BITMAP_AREA_SIZE, HASH_AREA_SIZE, SORT_AREA_SIZE, and SORT_AREA_RETAINED_SIZE. They need to be specified.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 176-182
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 17-18
Chapter 1: Oracle9i Database Administration and Management Features

---