因此，央行的冲销操作不但可行，而且有利可图。问题在于，外币贬值最终可能造成亏损。长远来看，低利率刺激下生成的支出终归会造成过剩需求和通货膨胀，如果经济和金融体系实行自由化就更是如此，但这一天还远没有到来。
因此，中国面临着重大的抉择：中国可以在国内吸纳过剩储蓄，使之直接服务于国民；另一方面，如果中国不愿进行这项调整，也有能力长期维持现状。如果中国决意进行调整，又应该如何抉择？是加快名义汇率升值还是允许通胀加速？中国应如何扩大需求？
How China managed to pin down the renminbi
China will do what it considers to be in its own interest. That should surely be self-evident. What is not self-evident is how it does - and should - identify that self-interest. That is almost always more difficult than naive realists tend to suppose. This is true of its policy towards North Korea. It is just as true of its policy towards the exchange rate.
The Chinese government seems to believe its interest lies in maintaining a highly competitive real exchange rate for as long as possible. The evidence also suggests it can do so for a long time. But should it do so?
Economic theory indicates that a fast-growing developing country should have an appreciating real exchange rate. This is known as the Balassa-Samuelson effect, after the late Bela Balassa of Johns Hopkins University and the Nobel laureate Paul Samuelson, who discovered it independently of each other.
The argument is straightforward. Economies contain two sorts of activity: tradeable - manufacturing and services that can be supplied readily at a distance; and non- tradeable - haircuts, childcare and so forth. With economic development, productivity in the former tends to rise faster than in the latter.
Assume, for simplicity's sake, that we are talking about a small country with a fixed exchange rate. Then the price of tradeables will be set in the world market and the domestic price will be the world price multiplied by the exchange rate. Prices of non- tradeables will rise relative to those of tradeables, because their relative unit labour costs will be increasing. This is why haircuts are cheap in poor countries and expensive in rich ones.
What does all this have to do with China? The answer, as Andrew Smithers of London-based Smithers &?Co, has pointed out, is that real exchange rate appreciation is the dog that has not barked.
Despite the modest change in exchange rate policy in July 2005, the nominal exchange rate of the renminbi has moved little since January 1994. Because China's inflation rate has been below that of the US for most of the past nine years, the tendency of the real exchange rate has been towards depreciation. According to JPMorgan, it has depreciated by about 7 per cent since January 1998 （see chart）.
Yet China seems to meet all the conditions for real exchange rate appreciation. As the International Monetary Fund notes in its September World Economic Outlook, productivity growth in industry has, on average, been about three percentage points a year faster than in services since 1979.
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