How would you interpret the following statement: “The curve depicting the relationship between national income per capita and life expectancy has shifted upward over time”?

A. Over time, even if a certain country’s national income does not change, it is likely that the country will observe a higher life expectancy due the impact of new knowledge and transfer of that knowledge across national borders.

B. Over time, even if a certain country’s life expectancy does not change, its national income will tend to grow anyway.

C. Over time all countries’ national incomes will grow, and that would lead to a higher life expectancy in turn.

D. Over time life expectancy in all countries tends to grow, and that would lead to higher national incomes too, as healthier people are more productive.