Final answer:
(option D) Velocity is a vector quantity that describes both the speed and direction of an object's movement. A change in velocity, which involves either speed, direction, or both, is known as acceleration. Velocity can be described as positive or negative based on direction.
Step-by-step explanation:
(option D) Velocity is the speed of an object in a particular direction. This means that velocity is a vector quantity, as it explains both the rate at which an object moves and the direction it is moving in. It is important to understand that velocity can be described as positive or negative depending on the direction, and it is independent of the path taken. The change in velocity, which can be a change in both magnitude or direction, is called acceleration. If a car is turning a corner at constant speed, it is still accelerating because its direction is changing.