我们知道这一点，因为过去曾经一再发生这一幕：贫穷的农村经济在一两代人的时间里摇身一变成为中等收入甚至高收入城市经济。
We know this because we have seen it happen repeatedly: a poor, agrarian economy transforms itself into a middle- or even high-income urban economy in one or two generations.