Which of the following statements is correct? An exception that has been declared must be referred to in the RAISE statement, or a PL/SQL error will occur. An exception that has not been declared must be referred to in the RAISE statement, or a PL/SQL error will occur. An exception that has been declared must not be referred to in the RAISE statement, or a PL/SQL error will occur. An exception that has been declared must be referred to in the SELECT statement, or a PL/SQL error will occur.