Final answer:
The ratio d/t for a car moving with a regular speed is constant and equal to the average speed, as the car maintains a steady pace without changing direction.
Step-by-step explanation:
For a car that moves with regular speed, the ratio d/t, which stands for distance (d) divided by time (t), is a measure of the car's average speed. In the case of a car traveling at a constant speed without changing its direction, this ratio remains constant over time. Therefore, the correct answer is that the ratio d/t is constant and equal to speed.
It's important to distinguish between average speed and instantaneous speed. The former is the total distance divided by the total time take, while the latter refers to the speed at a specific instant, which can be read from a car's speedometer. Additionally, when a car moves in a straight line at a constant speed, in physics terms, it’s said to be in linear motion with a constant velocity.