At an intersection with stop signs at all corners, right-of-way belongs to...?

Answer: C — The first vehicle to come to a complete stop

At a four-way stop intersection, the vehicle that arrives first has the right-of-way. This ensures a safe and orderly flow of traffic and avoids collisions. Option A is incorrect because the speed of a vehicle does not determine right-of-way. Option B is incorrect because the size of a vehicle does not affect right-of-way. Option D is incorrect because vehicles turning left must always yield to oncoming traffic and can only proceed once it is safe to do so. Therefore, the correct answer is C as it prioritizes the vehicle that arrived at the intersection first.