Final answer:
A straight line with a negative slope on a velocity-time graph indicates constant negative acceleration, meaning the object is slowing down consistently toward the reference point. Option a is correct.
Step-by-step explanation:
A straight line with a negative slope on a velocity-time graph indicates a consistent rate at which velocity is decreasing over time, which corresponds to constant negative acceleration. This means that the object is slowing down at a steady rate. In physics, the slope of the velocity-time graph represents the acceleration of the object.
Hence, a negative slope implies that the object is accelerating in the direction opposite to the direction of the initial velocity.
If the slope is constant and negative, the acceleration is constant in the negative direction. The acceleration vs. time graph for such motion would be a horizontal line at some negative value, illustrating that the acceleration does not change over time.
Therefore, the correct option in this context is constant acceleration toward the reference point (option A).