问题如下：
Which of the following is the main source of sustainable economic growth of a developed country?
选项：
A.the continuous capital investment
B.the growth of labor input
C.technological advances
解释：
C is correct. A developed country faces the limited growth in the labor input and capital investment. Technological advances allow it to overcome the limits imposed by diminishing marginal returns.
考点：影响一国经济增长的因素
解析：
发达国家在劳动力投入和资本投资（边际收益递减限制的考虑）方面增长有限。技术的进步使这类国家能够克服边际收益递减的限制。所以C选项正确。
Sustainability of Economic Growth 不是只和劳动力和劳动生产率有关么， 怎么选C？
