牙膏包装设计中，文字作为最主要的视觉表达要素之一，在包装设计是具有不可替代的作用。
Toothpaste packaging design, text, as a major factor of the visual expression in packaging design is an irreplaceable role.
这意味着国际贸易是要素国际流动的替代。
It implies that international trade is a substitute for the international mobility of factors.
经典的合约理论认为企业的本质在于用要素交易的合约替代产品交易的合约。
Classical contracting theory believes that the essence of enterprise is replacing the contracting of the product trade by the contracting of the factor trade.
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