Sometimes, China has fixed its exchange rate against the US dollar (when the value of the dollar goes up, the value of the yuan goes up, and when the value of the dollar goes down, the value of the yuan goes down).Find a chart of the USDCNY exchange rate and identify during which historical periods the exchange rate seems to have been fixed.Give a couple of reasons why the Bank of China might have managed its exchange rate in that way. Please provide one source.