Concept:Use the laws of logarithms. Write each fraction as a power of 2. Then use the power rule: logan=nloga.Explanation:Start with the given expression: log81+log21.Rewrite 81 and 21 as negative powers of 2.Since 8=23, we have 81=2−3.Since 2=21, we have 21=2−1.Therefore, log81+log21=log2−3+log2−1.Apply the power rule of logarithms: log2−3=−3log2 and log2−1=−log2.Add the results: −3log2+(−log2)=−4log2.The expression is now written in terms of log2.Answer:−4log2So the correct option is D. −4log2.