When a Teacher in a Private School Points Out to Her

Multiple Choice

When a teacher in a private school points out to her high school principal that since there are empty seats in all classrooms, the cost of additional students is really zero, she is using the

A) law of comparative advantage.
B) principle of marginal analysis.
C) theory of externalities.
D) notion of the cost decreases of the service sector.
E) concept of opportunity cost.