A. Fill in the blank: well, aquifer, dams, agriculture, recreation, subsidence, salt water intrusion. To access groundwater, are dug into . The primary use of groundwater by humans is for . Issues with aquifers include (sinking of sediment) and (contamination of salt water by the coast).

One drawback of voluntary trade is that it a.requires two groups to use a common language b.can make one group dependent upon another for necessary goods c.doesn't occur unless there is a shortage of goods for at least one group d.forces groups to rely on themselves to produce all the goods they need