Unit 3主要涉及跨境电商的货物运输和支付方式，学生需要掌握相关英语词汇和表达方式。

       以下是本单元答案：1. What are the most common methods of international shipping? – The most common methods of international shipping are air freight, sea freight, and express courier.2. What is the difference between X-ray and green channel customs clearance? – X-ray customs clearance involves the inspection of goods using X-ray machines, while green channel customs clearance is a faster process that requires less documentation.3. What are the advantages of using a letter of credit for international trade? – The advantages of using a letter of credit include increased security for both the buyer and the seller, as well as guaranteed payment once the terms of the letter of credit are met.以上是Unit 3的答案，希望对大家的学习有所帮助。

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