Why is light refracted when it passes from air to water? a) light slows down when it enters water b) forces from the water molecules bend the light c) the motion of the water bends the light d) the water is often cooler

The correct option is A. 
Refraction refers to the process of change in the direction of a wave propagation due to change in the transmission medium. When light travels from air to water, it slows down and this causes it to change direction slightly. The change in direction is called refraction. When light enters a denser medium, it bends more towards the normal line, the amount of bending that will be experienced depend on change in speed and angle of the incident ray.