Nate and Dylan Are Brothers

Multiple Choice

Nate and Dylan are brothers.They have to mow the lawn and clean their rooms before they can go to the high school football game.Nate mows the lawn and Dylan cleans up the rooms,and they make it to the football game on time.Which economic concept does this statement BEST represent?

A) "How Much" is a decision at the margin.
B) There are gains from trade.
C) Markets usually lead to efficiency.
D) One person's spending is another person's income.