The EMP table contains these columns: LAST_NAME VARCHAR2 (25) SALARY NUMBER (6,2) DEPARTMENT_ID NUMBER (6) You need to display the employees who have not been assigned to any department. You write the SELECT statement: SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMP WHERE DEPARTMENT_ID = NULL; What is true about this SQL statement ?（）

• A、The SQL statement displays the desired results.
• B、The column in the WHERE clause should be changed to display the desired results.
• C、The operator in the WHERE clause should be changed to display the desired results.
• D、The WHERE clause should be changed to use an outer join to display the desired results.