What were the problems the u. s. had under the articles of confederations?

What is the main idea of this excerpt

What would be considered a secondary source about the assasination of abraham lincoln

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