Final answer:
A change in speed of a wave causes it to change direction through the process of refraction.
Step-by-step explanation:
The change in speed of a wave can cause it to change direction through a process called refraction. Refraction occurs when a wave passes from one medium to another and its speed changes. When this happens, the wave bends or changes direction.
For example, when light waves pass from air to water, their speed decreases. This causes the waves to bend or refract towards the normal (a line perpendicular to the surface of the water). On the other hand, if the waves pass from water to air where the speed increases, they refract away from the normal.
So, the correct answer to your question is C) Refraction.