While the U$.$S$.$ GAAP determines what is included in financial reports of companies based in the United States, the GAAP used by companies based in other countries is determined by the governments of those countries. GAAP is different among countries due to the factors that influence the development of accounting and financial reporting. International GAAP is now used in many countries around the world, having been developed by the International Accounting Standards Board $($IASB$).$ The Board's international GAAP is called International Financial Reporting Standards $($IFRS$).$ There are many areas of difference between U$.$S$.$ GAAP and IFRS, but there are more similarities than differences. Which practice represents a substantive difference between U$.$S$.$ GAAP and IFRS?

a$.$ Presentation formats

b$.$ LIFO inventory costing method

c$.$ The use of metric vs$.$ English standards

d$.$ Harmonization of standards