A. When deciding whether to accept or not accept a special order, the focus needs to be on costs that will be different between one choice and the other. Variable costs will always be a consideration, as they would not exist if the order is not accepted. However, fixed costs are not relevant, because they will be the same whether the special order is accepted or not.

B. These costs are relevant to the decision, but they are not all of the relevant costs.

C. When deciding whether to accept a special order, fixed costs are not relevant as they will be the same whether the special order is accepted or not. However, direct fixed costs associated with the order will need to be considered, as they would not be incurred if the special order is not accepted.

D. Variable costs, fixed costs directly associated with the offer, and the opportunity costs of the idle capacity all need to be taken into consideration, as they are all relevant costs. These are all costs that will differ between the two alternatives of accepting the special order or not accepting the special order. Only the fixed costs of the product, which will be there whether the offer is accepted or not accepted, are not relevant to the decision.