Concept:Acceleration is the rate at which velocity changes with time.
Explanation:Acceleration is defined as
a=ΔtΔv.
So any situation where velocity changes is acceleration.
Velocity itself changes when speed changes, direction changes, or both change.
Therefore, a bus that is accelerating must always be changing its velocity.
Changing speed or direction are only specific ways of changing velocity.
Hence, the most general and correct condition is a change in velocity.
Answer:B. changing its velocity