问题：
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'
Examine the description of the EMPLOYEES table:
Which statement produces the number of different departments that have employees with last name Smith?（）
● 参考解析
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