试题题干
Look at the question.
In each question, which sentence is correct?
Payment to be made by cash on delivery. The invoice has to be paid （）
参考答案
正确答案：
试题解析
题目翻译：在交货时用现金支付。
题目中的on delivery“在交付时”，C选项的when“当···时”符合原文意思。