You set the following parameters in the parameter file and restarted the database：MEMORY_MAX_TARGET=0MEMORY_TARGET=500M PGA_AGGREGATE_TARGET=90MSGA_TARGET=270M Which two statements are true about these parameters after the database instance is restarted（）

• A、The MEMORY_MAX_TARGET parameter is automatically set to 500 mb.
• B、The pga_AGGREGATE_TARGET and sga_TARGET parameters are automatically set to zero.
• C、The value of the MEMORY_MAX_TARGET parameter remains zero until it is changed manually.
• D、The lower bounds of pga_AGGREGATE_TARGET and sga_TARGET parameters are set to 90 nb and270 mb， respectively