Final answer:
Dual command E) exists when a subordinate receives orders from only one supervisor, providing a clear line of authority.
Step-by-step explanation:
Dual command refers to a situation where a subordinate receives orders from only one supervisor. This means that a subordinate has a clear line of authority and knows exactly who they report to. Option E, 'It exists when a subordinate receives orders from only one supervisor', is therefore the correct answer. Dual command can help avoid confusion and strengthen order and discipline in an organization. It is not advocated by Henry Fayol, as stated in option D, and does not necessarily make assessing a manager's authority easy, as mentioned in option C. Dual command is focused on the clear line of authority for subordinates.