When using expenditure approach identity to measure the contributions of its components to GDP, the result is that net export only contributes a little to GDP, or import contributes negative to GDP.
在支出法恒等式中进口是负值，利用支出法恒等式测算其各组成部分对GDP的贡献，得到的结果是净出口仅对GDP作出很小的贡献，或者进口对GDP是负贡献。
The year of 1993 saw China turned from an oil export country into a net import one.
1993年，中国从石油出口国变为了石油净进口国。
Then, the economical effect of this system is analyzed and a mathematical model developed on the relationship between the import-export and the net profit of this system.
然后，对该系统进行了经济分析，建立了吞吐量与系统净盈利之间关系的数学模型。
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