Each quarter Sioux Company produces 30,000 units of a product that has variable costs of $60 per unit. Total fixed costs for the quarter are $990,000. A special order is received for 1,000 units at a price of $77 per unit. In deciding to accept or reject this special order, it is appropriate to consider the:
选项：

A: a. old fixed cost per unit of $33.00
B: b. difference between the offered price and the variable cost per unit
C: c. new fixed cost per unit of $31.94
D: d. difference between the two fixed costs per unit, which is $1.06