C. Earth's solid surface layer sits on a moving, semiliquid layer.
Explanation:
Earth is highly tectonically active because the solid layer of the earth sits on a moving, semi-liquid layer.
The earth's crust is broken into slabs. Together with part of the upper mantle, they form a layer called the lithosphere. These solid lithospheric bodies are called tectonic plates.
Under the plates is a semi-molten layer under great temperature.
As the molten layer moves, it carries the lithosphere on top of it.
This causes the movement of the plates in different directions.
The semi-liquid layer is called the asthenosphere
This is the reason why the earth is tectonically active.
