When all of the units produced are sold, the operating income is the same under both the absorption and variable costing methods. Assume no beginning and ending inventories. Which of the following gives the correct reason for the above statement?

A. Fixed manufacturing costs have not been considered when calculating the operating incomes.

B. All selling and administrative expenses have been recorded as period costs.

C. A portion of the fixed manufacturing overhead is still in the Finished Goods Inventory account.

D. All costs incurred have been recorded as expenses.