The correct answer is (b)- It slows down and builds up in height.
The speed of the water wave in shallow water is less than its speed in deep water. As the wave approaches the shore, the depth of the ocean decreases and it becomes shallower. The speed of the wave decreases, however, the frequency (number of waves produced per second) remains the same. The waves travel less distance per second, as their speed decreases in shallow waters. The waves, therefore bunch together and build in height as they approach the coast.
Thus, the waves slow down as they approach the coast and build in height.
