问题如下：
A fixed exchange rate regime in which the monetary authority is legally required to hold foreign exchange reserves backing 100% of its domestic currency issuance is best described as:
选项：
A.dollarization.
B.a currency board.
C.a monetary union.
解释：
B is correct.
With a currency board, the monetary authority is legally required to exchange domestic currency for a specified foreign currency at a fixed exchange rate. It cannot issue domestic currency without receiving foreign currency in exchange, and it must hold that foreign currency as a 100% reserve against the domestic currency issued. Thus, the country’s monetary base (bank reserves plus notes and coins in circulation) is fully backed by foreign 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 currency board 制度.
如果外币改为dollar是不是就是选择A呢
