Direct quotation is used in China, that is, one unit of foreign currency is used as the standard unit, such as how much RMB 1 is converted into, rather than how much RMB 1 is converted into. Most countries adopt direct quotation method, and a few countries adopt indirect pricing method. For example, Britain adopts indirect pricing method for other countries, that is, how much foreign currency 1 pound is exchanged; The United States adopts direct quotation to Britain and indirect labeling to other countries. Therefore, this topic chooses option a.