Which statement produces the number of different departments that have employees with last name Smith?

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’;