Reducing a rule to its principle says that, for the purpose at hand, the principle cannot be questioned or further derived unless you create a new rule.

通过将规则还原为原则，对于当前的用途，除非创建新规则，否则不能对原则进行质疑或进一步派生。

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However, exhibitors with hand-carried goods to the show, they should then declare to customs at the airport that their hand-carried goods are for exhibition purpose.

但是，如果展商携带手提展品参展的话，应在机场报关，申明货物用于展览之用。

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Ultimately, the use of metric in this country is a choice and we would encourage Americans to continue to make the best choice for themselves and for the purpose at hand and to continue to learn how to move seamlessly between both systems.

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