Concept:Double counting makes national income appear larger than its true value.Explanation:National income should include only the value of final goods and services.When the same commodity is counted more than once, its value is added repeatedly at different stages of production.This wrongly raises the total output value, causing an overestimation of national income.Incomplete data, wrong timing, and price changes also create errors, but double counting directly causes overestimation.Answer:D. double counting