问题如下图：
选项：
A. 
B. 
C. 
解释：
NO.PZ2016010802000216 a currenboar a monetary union. B is correct. With a currenboar the monetary authority is legally requireto exchange mestic currenfor a specifieforeign currena fixeexchange rate. It cannot issue mestic currenwithout receiving foreign currenin exchange, anit must holthforeign currena 100% reserve against the mestic currenissue Thus, the country’s monetary base (bank reserves plus notes ancoins in circulation) is fully backeforeign exchange reserves. 考点Exchange Rate Regimes 解析国家想发行本国货币，它必须持有100%的外汇储备。这是一种典型的 currenboar制度.请问这道题知识点在哪里 三个的含义是什么
如果外币改为llar是不是就是选择A呢
