在一个三个国家组成的世界里，中央银行固定一个汇率但允许其他汇率浮动。它能否用货币政策影响产出？它能否固定两个汇率？
In a three-country world，a central bank fixes one exchange rate but lets the other float. Can it use monetary policy to affect output？ Can it fix both exchange rates？