Concept:Simplify the given composite trigonometric function before differentiating.Explanation:Let y=sin2(cot−11+x1−x).Put θ=cot−11+x1−x.Then cotθ=1+x1−x.Squaring both sides, cot2θ=1+x1−x.Using 1+cot2θ=csc2θ, we get sin2θ=1+cot2θ1.Substitute the value: sin2θ=1+1+x1−x1=21+x.Hence y=21+x.Differentiating with respect to x, dxdy=21.Answer:21, which is option B.