Which of the following is not a way IFRS differs from U.S. GAAP for asset retirement obligations? OA. The nature of the obligation may be either economic or legal, not just legal. O B. The transaction may be accounted for using either the proportional method or remote method, not just the proportional method. O C. Valuation is discounted using a pre-tax rate, not an after-tax rate. OD. Valuation is based on edtimated costs, not fair value