Final answer:
A change in velocity occurs when there is a change in speed or direction. Scenarios B) Hector slows down and D) Hector turns onto a different road both depict changes in velocity because they include either a change in speed, direction, or both.
Step-by-step explanation:
The scenario which depicts a change in velocity is B) Hector slows down while biking along Main Street and D) Hector turns onto Bay Road while biking along Main Street. Velocity is a vector quantity, which means it has both magnitude and direction. Therefore, any change in speed or direction constitutes a change in velocity. When Hector slows down, he is changing the magnitude of his velocity. When he turns onto a different road, he is changing the direction of his velocity, even if he maintains the same speed.
Another way to consider a change in velocity is through acceleration. Acceleration occurs when there is a change in velocity, which can be a result of changing speed, changing direction, or both. If Hector is maintaining the same speed and riding in a straight line, there is no change in velocity, but as soon as he either decelerates (slows down) or makes a turn, his velocity changes.