Which statement BEST describes this photograph?
Segregation is a) constitutionally protected.
b) Integration should take place immediately.
c) Transportation is important in the United States.
d) People are protesting during the Civil Rights era.

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