外销员 英汉互译 ：repayment guarantee;optional port;互购；外汇储备；备用信用证

repayment guarantee 还款保证书（还款担保，还款保函）；
optional port 选择港；（任意港）；

Counter Purchase;
Foreign Exchange Reserves; Foreign Currency Reserves;
Stand - by L/C

我在网上找到答案的，我把链接给你
http://www.cqstudy.com/stjx/3957.html

repayment guarantee偿还的款项保证书
optional port可选择的港口
互购 mutual purchase
外汇储备 foreign exchange repertory
备用信用证spare letter of credit（L/C）