All of the following are reasons why China is unlikely to maintain high enough rates of productivity growth to catch-up with the standard of living in the United States except

a. Because of the low birth rate in China, the labor force will soon decline.

b. The United States invests more in research and development. Than does China.

c. Much of China’s growth is likely due to the transition from a centrally-planned economy to a market economy.

d. The Chinese migration of rural workers to more productive urban jobs.