The first method is that according to the relationship between supply and demand, selling RMB or buying USD will increase the supply of RMB or increase the demand for USD, thus making USD appreciate and RMB depreciate.

The second method is equivalent to reducing the supply of dollars, which will naturally keep the dollar at a higher price. On the other hand, the purchase of US Treasury bonds can promote the stability of the US economy and naturally maintain the strong position of the US dollar.