什么叫 an unopen letter of credit 如何定义的?

什么叫 an unopen letter of credit 如何定义的? What letter is an insect? Which letter is an insect? what letter is an insect? what letter is an animal? Which letter is an insect Which letter is an insect? What letter is an animai? the、a、an这叫什么词? write an e-mail与write a letter有什么区别? What letter is a question?What letter is an insect? letter 什么意思 letter什么意思 letter什么意思 letter delivery什么意思 Which letter is an insect?智力测试 what letter is an animal是什么意思 Which letter is an animal?快答啊