Which statement is true concerning write-downs under U.S. GAAP and IFRS?

a. GAAP allows inventory that has been written down to be revalued later at higher levels

b. IFRS allows inventory that has been written down to be revalued later at higher levels

c. GAAP and IFRS both allow inventory to be revalued higher once it has been written down

d. IFRS allows inventory revaluation only up to the point of a pervious write down