Final answer:
A car with a velocity to the left and acceleration to the right is decelerating.
Step-by-step explanation:
If a car's velocity is to the left and its acceleration is to the right, this means that the car is slowing down. Acceleration is defined as the rate of change of velocity. If acceleration is in the opposite direction of the velocity, it is acting to reduce the speed of the car, which is described as deceleration.
This situation matches from the given references, which illustrates a car moving to the left but slowing down because its acceleration is towards the right. Hence, the correct answer to the question, "Suppose a car's velocity is to the left, and its acceleration is to the right. Which of the following describes this car's motion?" would be D. Decelerating.