An earthquake generates a seismic wave that travels through several layers of the Earth's interior, shown below. The lithosphere is made out of solid rock, the mantle is a combination of solids and liquids, and the outer core is a liquid. The path of the seismic wave changes at the boundaries of each layer because A. the layers are different sizes. B. each layer is made out of the same material. C. seismic waves always change direction after a few miles. D. each layer has different properties.