Answer: C) This is an example of refraction and not diffraction.
Explanation: The reason for the straw to appear bent at the water's surface is because of the process of refraction. Light travels at different speeds in different medium because of the varying densities.
The light travels from air to water and thus the difference in speed results in an apparent shift of the position of part of straw under water and thus the part appears broken.
Reflection is the the return of sound or light energy from the surface without absorbing it.
Diffraction is the phenomenon which occurs when the wave encounters an obstacle.