Concept:Standard of living is best measured by the average income per person, not by total national income.Explanation:Comparing the number of industries or military strength does not reflect people's economic well-being.Total national income alone is misleading because countries have different population sizes.Gross national product per head gives income per person after dividing total income by the population.This makes it a fair and accurate measure for comparing living standards between two countries.Answer:D. gross national product per head