Whether Studying the Output of the U

Whether studying the output of the U.S. economy or how many classes a student will take, an unifying concept is that:

A) wants are limited and resources are unlimited, so trade-offs are unnecessary.
B) wants are unlimited and resources are scarce, so trade-offs have to be made.
C) wants are limited and resources are unlimited, so trade-offs have to be made.
D) both wants and resources are unlimited.