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 UNIQE (dept_id) FROM employees WHERE last _name='smith';