A wave is any movement that carries energy. Some waves carry energy through water. Others carry energy through gases, like air, or solid materials. If you drop a rock into a pool of water, a wave, or ripple of energy, skims across the pool's surface. In the same way, an underwater earthquake can release energy into ocean water. Then it carries a giant wave, or tsunami, across the surface until it hits land.
A. to inform readers about different kinds of waves
B. to persuade readers to throw rocks into the water
C. to entertain readers with the legend of Wally Wave
D. to teach readers how to use a surfboard to ride waves