A company has three sales departments (local, regional, and national) at each of several locations across the United States. Each local sales department has 120 employees. The company wants to survey its employees to determine the most effective sales method. Which sample should the company use to arrive at the most reliable conclusion?

A 24 employees from one sales department at one location

B 24 employees from one sales department at each location

C 24 employees from each sales department at one location

D 24 employees from each sales department at each location