Concept:Revenue is the product of tax rate and consumption. Use successive percentage change formula.Explanation:Let original revenue be 100 units.Tax is reduced by 10%, so tax factor becomes 0.9.Consumption increases by 10%, so consumption factor becomes 1.1.New revenue =100×0.9×1.1=99.Change in revenue =99−100=−1.Thus, percentage change K=−1%.Using the formula: x+y+100xy​=−10+10−100100​=−1.Answer:K=−1%Correct option: C. −1