What defines an aquifer?

An aquifer is defined as a geological formation that can store and transmit groundwater, allowing for the extraction of water for various uses such as drinking, irrigation, and industrial purposes. It typically consists of permeable materials like sand, gravel, or limestone that enable water to flow through them. This ability to hold and move water distinguishes aquifers from other formations, making them critical sources of freshwater for ecosystems and human activities.

The other options describe different geological or water-related features, but they do not meet the criteria of an aquifer. Solid rock, for example, may not have the necessary porosity or permeability for water storage or flow. Natural ponds or lakes are surface water bodies rather than underground formations where groundwater is stored, and a man-made water reservoir is a constructed entity designed to hold water, which also does not define an aquifer's natural and geological characteristics. Thus, the definition of an aquifer is specifically tied to its ability to store and supply groundwater.