Answer:
The correct answer is letter "D": explains most of the differences in the standard of living across countries.
Explanation:
Productivity is an economic term that describes the relationship between output and inputs needed to produce those outputs. It measures effectiveness. The total production of a country given a period is calculated in its Gross Domestic Product (GDP).
When the GDP is divided by the total population of a country it is called GDP per capita which reflects the average expenditure of individuals. This metric allows having an idea of what the lifestyles of those people are. Usually, smaller wealthy countries such as Switzerland have higher GDP per capita showing a better quality of life.