If a blind pedestrian is waiting at a crosswalk with a white cane or a guide dog, you must:

Answer: A — Haunt the horn

You must honk your horn when a blind pedestrian is waiting at a crosswalk with a white cane or a guide dog. This is to alert them to the presence of a vehicle and ensure their safety. Option B is incorrect because it advises against using the horn or revving the engine, which could confuse or startle the pedestrian. Option C is incorrect because revving the engine serves no practical purpose in this situation. Option D is incorrect because it suggests avoiding the situation altogether, rather than properly accommodating and respecting the rights of the blind pedestrian.