Which of the following is the basic measure of a nation's economic growth rate?

A. standard of living over a given period of time

B. Nonmarket activities over a given period of time

C. leading indicators over a given period of time

D. percentage change of real GDP over a given period of time

D is the correct answer. The standard of living does not necessarily deal with the nation's economy, neither does the nonmarket activity. 'Leading indicators' could mean many things and is too general to be a satisfactory answer. Real GDP is a measure of the nation's economy, and the percent changed over time will show if that measure has grown or decayed.