Concept:The relation between x and y can be simplified before differentiating.Explanation:Given x=sinθ and y=sin3θ.Since y=(sinθ)3, we get y=x3.Differentiating with respect to x: dxdy=3x2.Differentiating again: dx2d2y=6x.At θ=2π, x=sin2π=1.Therefore, (dx2d2y)θ=2π=6(1)=6.Answer:The correct option is D. 6.