The loss of a key customer has temporarily caused Bedford Machining to have some excess manufac- turing capacity. Bedford is considering the acceptance of a special order, one that involves Bedford's most popular product. Consider the following types of costs: 

I. Variable costs of the product 

II. Fixed costs of the product 

III. Direct fixed costs associated with the order 

IV. Opportunity cost of the temporarily idle capacity 

Which one of the following combinations of cost types should be considered in the special-order acceptance decision?

a. I and II

b. I and IV

c. II and III

d. I, III, and IV