Answer
Wind
Water movement
A hill
Explanation.
The question does not specify it is the acceleration of what is to be accelerated. So my answer will be general. Acceleration is the change of velocity with time.
Wind can cause acceleration of sound. If the sound is travelling in the direction of sound, its speed wound increase. The reverse is also true.
Water movement can also cause acceleration. When a bout is moving in the direction of water movement, then it will be expected that the resultant speed of the bout to be higher. If the bout was moving against the water movement, its speed would be decreased.
A hill would reduce the speed of a moving vehicle. This is also an acceleration that is negative (deceleration).
A stop light and a flat road cannot cause acceleration.
