Which of the following statements about the use of differential analysis in decision making is true? O If a special-order decision requires the use of capacity that is not idle, opportunity costs are zero. O It is always profitable to continue processing joint products after the split-off point if their total revenues exceed the joint costs. O An avoidable fixed production cost incurred before the split-off point in a joint process is a relevant cost in a sell as-is or process further decision. O Per-unit variable costs are not always differential costs. O None of the above statements are true.