For any \({\rm{\theta }} \in \left( {\frac{{\rm{\pi }}}{4},{\rm{\;}}\frac{{\rm{\pi }}}{2}} \right),\) the expression 3(sin θ – cos θ)4 + 6(sin θ + cos θ)2 + 4sin6 θ equals

• A. 13 – 4 cos2 θ + 6 sin2 θ cos2 θ
• B. 13 – 4 cos6 θ
• C. 13 – 4 cos2 θ + 6 cos4 θ
• D. 13 – 4 cos4 θ + 2 sin2 θ cos2 θ