What is an aquifer? a. a river dam b. a natural underground water supply c. an environmental hazard caused by drilling d. a state agency that monitors water usage (the answer is B, i just wanted to put the question)

a natural underground water supply

Explanation:

An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt). Groundwater can be extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology.