The most easily polluted groundwater reservoirs are

a. sewage plant reservoirs.
b. water-table aquifers.
c. salt reservoirs.
d. artesian wells.

The right option is B. water-table aquifers

Water-table aquifers are underground layer of water whose water table is at atmospheric pressure and is not below a confining layer. Water-table aquifers are susceptible to drought conditions and pollutants because they are usually closer to the earth's surface. Water-table aquifers can be polluted by naturally occurring mineral and metallic deposits in rock and soil, manufactured chemicals such as fertilizers, and dumps or landfills. When ground water pollutants reach a water-table aquifer, they make the water unclean and unusable for decades.