p303 dornbush edition9

汇率问题我一直搞不明白

第二段：For example , if the United States were running a deficit in the balance of payments vis-a-vis Japan ,and thus the demand for yen in exchange for dollors exceeded the supply of yen in exchange for dollars from Japanese ,the Bank of Japan would buy the excess dollars,paying for them with yen.

balance of payment 怎么译？

这段我不懂，我们国家也实行固定汇率制，我想这个例子比较实用，可是看不懂，着实烦恼，请精通的人用简明易懂的语言帮我理解理解这段话，谢谢！

还有第三段：

Fixed exchange rates thus operate like any other price support scheme ,such as those in agricultural markets.Given market demand and supply ,the price fixer has to make up the excess demand or take up the excess supply.In order to be able to be ensure that the price (exchange rates)stays fixed ,it is obviously necessary to hold an inventory of foreign currencies ,or foreign exchange ,that can be provided in exchange for the domestic currency.

什么含义？