When is it permitted to use the horn for giving a warning signal in an urban road?

1. It is only allowed to use an air horn.
2. It is always allowed to use the horn, provided that the signal is given in a continuous and uniform manner.
3. Correct answer: It is only allowed to use the horn in order to avoid imminent danger that cannot be prevented in any other way.
4. It is always allowed to use the horn in an urban road.

WhyIn a city you may sound the horn only to avoid a danger that cannot be prevented any other way. Not just like that.