[单项选择]

The differences in living standards around the world are vast In 1993, the average American had an income of about ＄25,000. In the same year, the average Mexican earned $7,000, and the average Nigerian earned. ＄1,500. Not surprisingly, this large variation in average income is reflected in various measures of the quality of life. Changes in living standards over time are also large. In the United States, incomes have historically grown about 2 percent per year (after adjusting for changes in the cost of living). At this rate, average income doubles every 35 years. In some countries, economic growth has been even more rapid. In Japan, for instance, average income has doubled in the past 20 years, and in South Korea it has doubled in the past 10 years.
What explains these large differences in living standards among countries and over time The answer is surprisingly simple. Almost all variation in living standards is attributable to differences in countries’ productivi
A. Labor unions.
B. Minimum-wage laws.
C. Rising productivity.
D. Favorable public policy.