Explains why anyone in the classroom can hear that loud teacher across the hall even though the door is barley cracked open

A. Reflection

B. Refraction

C. Diffraction

The answer is D ...

Diffraction:

Diffraction describes how waves bend, or change direction, as they travel around the edges of obstacles. Diffraction occurs in water waves, sound waves, and light waves, but the amount of diffraction depends on the size of the obstacle or opening in relation to the wavelength of the wave.