In which area do the united states' state and federal governments share power?
a-collecting taxes
b-declaring war
c-forming international treaties
d-granting titles of nobility

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