Final answer:
A aquifer is a porous geological formation that stores and permits the flow of groundwater, with 'a. Aquifer, Porous' being the correct answer choice.
Step-by-step explanation:
A aquifer is a porous geological formation that stores and allows the flow of groundwater. Therefore, the correct answer to the question is a. Aquifer, Porous. Aquifers are critical to our water supply, as they are underground layers that can hold water and allow water to pass through them. These geological formations' ability to store and conduct water is determined by their porosity and permeability. For example, sedimentary rocks such as sandstone and limestone are known to be good aquifers due to their high porosity and interconnected pore spaces. In contrast, impermeable rocks like shale, or un-fractured igneous and metamorphic rocks, create confining layers that impede water flow.