Lithosphere includes all the Earth known to us: the mountains, the ground we walk on, etc. It's solid - else we would not be able to walk on it! the more inner layers of Earth are liquid, but lithosphere, the outermost layer is solid. The tectonic plates are not floating on the lithosphere - they form the lithosphere! So the correct answer is A - it is solid and composed of crust and upper mantle (outer later)
