You should use your horn when

A. Your view of the road is obscured by a vehicle ahead of you

B. You're following a long line of cars

C. There is no other way to avoid a collision

Your answer is C, there is no other way to avoid a collision. A horn on a car is not meant to honk at bad drivers or to tell cars ahead to move faster, a horn on a car is meant to alert other drivers if a crash is likely or you are unable to do any other crash-preventing actions.

The answer is C. That's what I think