Correct answer: B. Lithosphere
Explanation: Direct answer: Option B, lithosphere. Earth can be understood through layers. The lithosphere is the hard, rigid outer shell made mainly of the crust and the uppermost mantle. It is broken into large pieces called tectonic plates. These plates move slowly over the softer, weaker asthenosphere below them. Option B is correct because plate tectonics studies the movement and interaction of lithospheric plates. Option A, atmosphere, is the layer of gases around Earth and is not a solid plate layer. Option C, hydrosphere, means Earth’s water, including oceans, rivers and groundwater; water is not the material forming tectonic plates. Option D, inner core, is the very hot central solid part of Earth and is far below the plates. Memory cue: “litho” means rock, so lithosphere is the rocky shell carrying plates.