Which of the following is an example of a sunk cost?

Select one:

a. The firm pays to replant trees following the clear cutting of 1,000 acres during a timber harvest.

b. The firm spends $20 million on heart medication research and discovers a promising drug.

c. The firm replaces a piece of manufacturing equipment to maintain current manufacturing capacity.

d. A bank opens a new office, and the new office leads to a decline in deposits at the bank's other offices.

e. All of the above are examples of sunk costs.