Answer:D. It is a component in the Earth System that holds material for a period of time.
Explanation: A reservoir is a component in the earth that holds materials which can be water, weathered rocks and other substances for a given period of time. The reservoirs can be Natural or artificial an example of reservoir can be seen in the form of man made lakes as seen in different parts of the world. Reservoir helps to store materials or water for later use,the stored materials can be of great importance to the life of man.
THE ATMOSPHERE IS AN EXAMPLE OF A RESERVOIR FOR GASES.