[单选题]Which statement about Automatic Memory Management 

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.