In the past, China's imports and exports were denominated in foreign currencies, and all the businesses used in your book were denominated in foreign currencies.

After the cross-border RMB settlement business was launched in China in 2009, some import and export businesses were denominated in RMB. China enterprises pay RMB for imported goods, and overseas exporters get RMB and convert it into foreign currency overseas.

Let's talk about why the local currency will appreciate when a country has a trade surplus. For example, in recent years, China's balance of payments has been in a surplus, and the US dollar income is far greater than that of foreign countries, so the total amount of US dollars in China has increased, but most of the increased US dollars have to be converted into RMB, which leads to an increase in the transactions of selling US dollars to buy RMB in the market, which will lead to a decline in the price of US dollars against RMB, that is, the depreciation of US dollars and the appreciation of RMB.