Final answer:
The standard of living in two countries with the same total output can differ primarily due to population size, which affects the GDP per capita, a common measure of economic welfare. However, other factors like health, education, and human rights also impact living standards.
Step-by-step explanation:
If Country A and Country B have the same total output, the standard of living in these two countries can still be different due to various factors. The option that correctly identifies one such factor is D. population size.
A common way to compare the economic welfare or standard of living between countries is to look at Gross Domestic Product (GDP) per capita, which is the GDP divided by the population. However, per capita GDP does not fully account for the quality of life. Other factors impacting standard of living include health, education, human rights, crime and personal safety, and environmental quality.
It is important to also note that different countries may have very different population sizes, which affects how we perceive the overall wealth and resources available to individuals within a country.