An underground layer of rock or sand that holds water is called a(n) a. geothermal layer b. glacier c. reservoir d. aquifer

D. aquifer

Explanation:

An aquifer is a layer of the water that is found underground water reserves and is bearing the preamble rocks and the rocks fractures and the unconsolidated material. The study of the water flow is characterized by hydrogeology.  The other terms include the aquitard and that is defined for low permeability. It can be up to 30,000 feet deep. And is used to supply the fresh water for irrigation and the other facilities. They are two types of unstratified and stratified types, confined and undefined type. The porosity of the soil like that of the sandstone is important for the formation of the groundwater table.

Answerequatorial guinea,gabon, and western sahara;