please answer correct

ABC Ltd is deciding whether or not to accept a special order for 500 units. It has no spare capacity to accept the order. If the order is accepted the incremental revenue would be $10,000 and the incremental cost to make the order would be $8,000. In deciding whether or not to accept the order, the firm should consider: a the incremental revenue = $10,000 and the incremental cost = 58,000, only b the opportunity cost of accepting the order as part of the impact on profits c the unavoidable costs d all manufacturing costs only