Mark is an engineer who has designed a telecommunications device. He is convinced that there is a big potential market for the device. Accordingly, he has decided to quit his present job and start a company to manufacture and market the device. Mark purchased a machine two years ago to make experimental boards. The machine will be used to manufacture the new board. The cost of this machine is:
a. a period cost
b. an opportunity cost
c. a sunk cost
d. a differential cost
