When fungible goods of different countries of origin are commingled the country of origin of the goods:

(a) Is the countries of origin of those commingled goods; or

(b) If the good is fungible, has been commingled, and direct physical identification of the origin of the commingled good is not practical, the country or countries of origin may be determined on the basis of an inventory management method provided under the appendix to part 181 of the Customs Regulations.