4. The People's Republic of China has had a large trade surplus in recent years. What is the most likely explanation of this surplus? a. China has a high rate of inflation, which reduces the value of its currency. b. China has a large supply of labour, so low wages give it a competitive edge. c. China has many trade barriers, which restrict the ability of other countries to sell their products in China. d. China has a large amount of saving relative to domestic investment