Which of the following statements is true regarding the initialization parameter DIAGNOSTIC_DEST?
A.The default value is the value of the environment variable $ORACLE_HOME; if $ORACLE_HOME isn't set, then the default is set to $ORACLE_BASE.
B. The default value is the value of the environment variable $ORACLE_BASE; if $ORACLE_BASE isn't set,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.
When $ORACLE_BASE is set,it is the default value for DIAGNOSTIC_DEST.