问题描述：
谁能给我讲讲upon的用法
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例如：the declaration formalities may be gone through with the customs in the ports upon the approval of the competent customs in the park.
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例如：the declaration formalities may be gone through with the customs in the ports upon the approval of the competent customs in the park.
问题解答：
我来补答展开全文阅读