Which of the following statements is true regarding the initialization parameter DIAGNOSTIC_DEST?()  <br /> The default value is the value of the environment variable $ORACLE_HOME; if $ORACLE_HOME isn’t set  
A、 then the default is set to $ORACLE_BASE The default value is the value of the environment variable $ORACLE_BASE; if $ORACLE_BASE isn’t set,
B、 then it is set to $ORACLE_HOME
C、 DIAGNOSTIC_DEST is always equal to $ORACLE_HOME
D、 DIAGNOSTIC_DEST is always equal to $ORACLE_BASE