"hope is the thing with feathers"

what is the theme of this poem?

1. without hope, people are not a human.

2. hope does not give up, even when life is difficult.

3. people hope for things that do not come true.

4. spring is a hopeful season.

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