To demonstrate why a quarter at the bottom of a pool of water is never where you expect it to be, the student should focus on how light behaves when it moves from air into water. The most relevant feature for this model is:
D. Arrows showing bending light waves as the light enters the water from the air.
This feature will illustrate the refraction of light, which is the bending of light rays as they enter a different medium (in this case, from air to water). Refraction is responsible for the apparent displacement of the quarter's position when viewed from above the water's surface.
While features A, B, and C relate to light behavior, they do not directly address the phenomenon that causes the quarter to appear in a different position than its actual location. Arrows showing light waves bouncing off the surface (A) and spreading out (B) provide useful context about how light interacts with different mediums, but they do not exemplify the main reason for the misperception. Similarly, multiple light waves traveling straight through the water (C) does not capture the bending effect either.
Therefore, option D is the best choice to effectively communicate the concept of refraction and explain why the quarter appears altered from its true position at the bottom of the pool.