Which type of U.S. government security is a kind of zero-coupon security?

Which of the following statements is TRUE about scarcity?

A) Both rich and poor people face the problem of scarcity. B) Scarcity exists only when supply is insufficient to meet demand. C) Scarcity exists only when a shortage exists. D) Scarcity can be eliminated when a country becomes richer.

Assume that labor is the only variable input and that an additional input of labor increases total output from 72 to 78 units. If the product sells for $6 per unit in a perfectly competitive market, then the marginal revenue product of this additional worker is:

a. $78. b. $72. c. $36. d. $39. e. $6.