053-639

You want to enable automatic PGA memory management in your database. Which setting is required to achieve this?
A. Set MEMORY_TARGET to zero
B. Set the STATISTICS_LEVEL parameter to BASIC
C. Set the WORKAREA_SIZE_POLICY parameter to MANUAL
D. Set the PGA_AGGREGATE_TARGET parameter to nonzero value

关于PGA_AGGREGATE_TARGET参数说明
http://blog.itpub.net/10867315/viewspace-2131276/

Automatic PGA Memory Management:
When automatic memory management is disabled and PGA_AGGREGATE_TARGET is set
to a nonzerovalue,the database uses automatic PGA memory management.

In this mode, the PGA_AGGREGATE_TARGET specifies a target size for the instance PGA.
The database then tunes the size of the instance PGA to this target and dynamically tunes the sizes of individual PGAs. If you do not explicitly set a target size, then the database
automatically configures a reasonable default.