Concept:The hydrosphere is the water layer of the Earth, including oceans, seas, lakes, and rivers.
Explanation:The Earth's surface is divided into different spheres.
The stratosphere and ionosphere are layers of the atmosphere, not water bodies.
The biosphere is the zone where living organisms exist.
The hydrosphere covers the part of the Earth's surface occupied by water, including oceans and seas.
So the water-covered portion of the Earth's surface is called the hydrosphere.
Answer:Option C. Hydrosphere.