问题如下：
The sustainable growth rate is best estimated as:
选项：
A.the weighted average of capital and labor growth rates.
B.growth in the labor force plus growth of labor productivity.
C.growth in total factor productivity plus growth in the capital-to-labor ratio.
解释：
B is correct.
Output growth is equal to the growth rate of the labor force plus the growth rate of labor productivity, i.e. output per worker. Unlike total factor productivity, output per worker is observable, so this is the most practical way to approach estimation of sustainable growth.
考点： Sustainable growth rate
解析：stainable growth rate 可以表示为 the growth rate of labor productivity 与 the growth rate of the labor force的加和。
蓝色框的两个有啥区别？
