How important are the seismic waves in the study of earth's interior

Knowing how the waves behave as they move through different materials enables us to learn about the layers that make up the Earth. Seismic waves tell us that the Earth's interior consists of a series of concentric shells, with a thin outer crust, a mantle, a liquid outer core, and a solid inner core.

the answer is d. made landless peasants that owners of large haciendas

the rub-al-khali is also known as the arabian desert and the "empty quarter"