【单选题】Examine the description of the EMPLOYEES table: 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';