Upon approaching a stop sign, a driver must:
Answer: D — Stop, and when it is safe to do so, proceed.
When approaching a stop sign, a driver must come to a complete stop before proceeding. Option A is incorrect because the driver does not need to sound the horn at a stop sign. Option B is also incorrect because even if the way appears clear, the driver must still come to a complete stop. Option C is incorrect because the driver does not need to sound the horn before proceeding. Option D correctly states that the driver must stop and then proceed when it is safe to do so. This is important for safety and to ensure that the driver has enough time to assess the situation before proceeding.