Which of the following statements is true regarding the initialization parameter DIAGNOSTIC_DEST？（） 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
DIAGNOSTIC_DEST is always equal to $ORACLE_BASE