The correct answer is A. 10.
The caution order must be issued within 10 minutes if the patrol man does not turn up. This is because the patrol man is responsible for ensuring the safety of the area, and if he does not arrive within a reasonable time, it may be necessary to take additional measures to protect the public.
Option B is incorrect because it is too short a time frame. It is not realistic to expect the patrol man to arrive within 5 minutes, especially if he is located far away from the scene.
Option C is incorrect because it is too long a time frame. If the patrol man does not arrive within 15 minutes, it may be necessary to take additional measures to protect the public, such as calling the police or issuing a warning to the public.
Option D is incorrect because it is the same as option C.