Which of the following statements is correct?
a. The competitive rental rate of machines (capital) is the sum of forgone interest and depreciation costs the machine’s owner must pay for one period.
b. In the case of machines that do not depreciate, the competitive rental rate of machines (capital) is equal to forgone interest for an infinitely long time.
c. The competitive rental rate of machines (capital) is the cost borne by firms whether they rent the machines they use or own them.
d. All of the above.