Which of the following would not be relevant to a make-or-buy decision?

(a) Allocated portion of depreciation expense on existing facilities.

(b) Variable cost of labor used to produce products currently purchased from suppliers.

(c) Warehousing costs for inventory of completed products (inventory levels will be constant regardless of whether products are purchased or produced).

(d) Cost of materials used to produce the items currently purchased from suppliers.

(e) Property taxes on the factory building.