Which statements about the MEMORY_TARGET initialization parameter are true?（） (Choose all that apply.)

A. MEMORY_TARGET can be increased up to the value of MEMORY_MAX_TARGET, if MEMORY_MAX_TARGET is set to a value greater than zero
B. MEMORY_MAX_TARGET defaults to a value of zero if MEMORY_TARGET is not set
C. MEMORY_TARGET represents the total amount of memory that can be allocated to SGA and PGA memory structures.
D. MEMORY_TARGET is static and cannot be modified without shutting down the instance