Concept:When a fraction has a negative exponent, take its reciprocal first; the square root means raising to the power 21.Explanation:The expression is (641)−32.First compute the square root: 641=81, since 8×8=64.So (641)−32=(81)−32.A negative exponent flips the base: (81)−32=832.Now 8=23, so 832=(23)32=23×32=22=4.Answer:D. 4