Concept:The value added method prevents the same output from being counted more than once in national income.Explanation:In measuring national income, each firm’s output may be used as an input by another firm.Counting the full value of output at every stage would lead to double counting.The value added method considers only the extra value created at each stage of production.This extra value is the difference between a firm’s sales and the cost of intermediate goods purchased from other firms.Summing these value additions across all firms gives the total value of final output without duplication.Answer:B. avoid multiple counting of output.