Concept:The best measure for comparing living standards across countries is per capita income.Explanation:Per capita income is the average income earned by each person in a country in a given year.It is calculated as:Per capita income=Total populationNational incomeBy dividing total national income by population, per capita income accounts for differences in population size between Nigeria and Ghana.For example, a country with a higher total income may still have a lower standard of living if its population is very large.Therefore, per capita income gives a more accurate basis for comparing the standard of living between Nigeria and Ghana.Answer:B. per capita income