Which statement about Automatic Memory Management with Oracle 11g is true？（）  

• A、 You cannot specify MEMORY_TARGET if you explicitly specify SGA_TARGET or  PGA_AGGREGATE_ TARGET values that are greater than zero in your parameter file.
• B、 Oracle can reallocate memory between the SGA and PGA automatically as needed.
• C、 To use Automatic Memory Management， you must explicitly set both the MEMORY_TARGET and MEMORY_MAX_TARGET parameters in your parameter file.
• D、 You can set the MEMORY_TARGET parameter to a maximum value of the current SGA size plus the current PGA size.