Which of the following best describes what an aquifer is? a. an unsaturated, losing stream bed or stratum below a spring.
b. the porous and permeable, saturated cone of depression in an aquitard. c. a saturated, porous and permeable layer or stratum. d. a layer or stratum in which groundwater flows downward to the water table.

The statement "a saturated, porous, and permeable layer or stratum" best describes the aquifer.

An aquifer is a liquid layer of porous rock, rock fractures, or uncemented equipment near the ground. A well can be used to extract groundwater from aquifers. Hydrogeology is the study of aquifer water flow and characterization.

Therefore, the correct option is c.

To know more about aquifers, refer to the link below:

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b. the porous and permeable, saturated cone of depression in an aquitard.

Explanation:

An aquifer is an underground layer of water, surrounded by a porous, and saturated layer of water bearing rock. The aquifer is lined by a layer of bed of low permeability along its length. This layer is called an aquitard, and it usually forms a depression.

d. stage 4

explanation:

the existence of some kind of demographic transition is widely accepted in the social sciences because of the well-established historical correlation linking dropping fertility to social and economic development.[1] scholars debate whether industrialization and higher incomes lead to lower population, or whether lower populations lead to industrialization and higher incomes. scholars also debate to what extent various proposed and sometimes inter-related factors such as higher per capita income,lower mortality, old-age security, and rise of demand for human capital are involved.[2]