The Directors of BB Limited Are Quoting for a Construction

The directors of BB Limited are quoting for a construction contract and are drawing up a list of the expected costs for the contract. Which one of the following costs is not a relevant cost for this quotation?

A) The firm's own plant and machinery bought four years ago for £35,000 and which will be used on site during the construction contract.
B) Crane hire at a daily rate of £500 which will be charged to the business on this contract.
C) Spare materials that can be sold for £600.
D) The £10 hourly rate paid to the workforce on the basis of the number of hours worked on a job.