Examine the description of the EMPLOYEES table: EMP_ID NUMBER(4) NOT NULL LAST_NAME VARCHAR2(30) NOT NULL FIRST_NAME VARCHAR2(30) DEPT_ID NUMBER(2) Which statement produces the number of different departments that have employees with last name Smith?（）

A.SELECT COUNT(*) FROM employees WHERE last_name='Smith';

B.SELECT COUNT(dept_id) FROM employees WHERE last_name='Smith';

C.SELECT DISTINCT(COUNT(dept_id)) FROM employees WHERE last_name='Smith';

D.SELECT COUNT(DISTINCT dept_id) FROM employees WHERE last_name='Smith';

E.SELECT UNIQUE(dept_id) FROM employees WHERE last_name='Smith';