Examine the parameter setting in your database: 
Which statement is correct about the database?
A. Automatic memory management is disabled because PGA_AGGREGATE_TARGET and SGA_TARGET are not set
B. The instance is started but the database will not be opened until PGA_AGGREGATE_TARGET and SGA_TARGET are set
C. The database is opened but users cannot perform transactions until PGA_AGGREGATE_TARGET and SGA_TARGET are set
D. Automatic memory management is enabled and, as per policy, 60% of the memory for System Global Area (SGA) and 40% of the memory for Program Global Area (PGA) will be distributed at startup
由于设置了 memory_target，所以 AMM 是启用的。数据库是可以打开，并且用户可以执行事务，AB,C 错误
一般情况 PGA 20%，对于 DSS 系统，这个值可以更高可以达到 70%，D 对。