The correct answer is (b.) spilling breaker. A spilling breaker, which is a type of wave that results from a moderately sloping coastal region. The wave which can be a spilling breaker usually breaks slowly as it reaches the nearest shore.
The spilling breaker is also known as surf wave is an over-steepened wave in which the unsteady top of the wave tumbles down the front of the waveform as it progresses towards the shallower water. This results in a gradual reduction of the height of the wave unless it moves up the beach as swash. The kind of wave, which arises from a moderately sloping coastal region will be a spilling breaker, as it is a common wave related to moderate beach gradient.
