Answer:
B. The amount paid 4 years ago for an existing building to be used in the project
Step-by-step explanation:
As this value is sunk it should be ignored. The company should think on project for the building considering his market value.
Also, the amount of working capital (used in the project in form of accounts receivable, account payable, prepaid and others) is important as this release increase the cash flow of the project.
The salvage value is also important as will provide cash flow as well.
As general rule, always look into the future to evaluate the projects never at historic cost.