Audio signals may be used by drivers of public vehicles:
To gain an advantage over other road users.
In the settlements to warn other drivers about the intention to overtake.
When it is necessary to prevent a traffic accident.✓Correct answer
In all the cases above.
Explanation
An audible warning may be given wherever it is necessary to prevent a road accident. It may not be used merely to gain priority, and warning another driver of an intended overtake is permitted only outside built-up areas. Those limits also mean that treating every listed use as permissible would be too broad.