unofficial rate of exchange

例句：

1. 1. The company's decision to change the currency exchange rates is causing a lot of controversy.
   公司决定改变汇率，引起了很多争议。
2. 2. The unofficial rate of exchange between the two countries has been steadily increasing.
   两国之间的非官方汇率一直在稳步上升。
3. 3. The unofficial rate of exchange between the two currencies is often used by traders for their transactions.
   两种货币之间的非官方汇率通常被交易者用于他们的交易。