The earth is made up of many interacting system which are quite dynamic in nature. The earth is sub divided into four components which are THE ATMOSPHERE, THE HYDROSPHERE, THE BIOSPHERE AND THE GEOSPHERE. These are the separate systems that made up the earth system.
The hydrosphere is make up of all the water components on the earth surface and how the water cycle through nature. The atmosphere refers to the layers of gases that surround the planet earth while the biosphere refers to the living components on the earth surface. All these systems interact together to keep life existing on earth.
The answer would be D because it leaves you thinking about what will happen next. Hope this helped you out .
Both. You can use it as singular or plural.
