$\cos 13^{\circ} \sin 17^{\circ} \sin 21^{\circ} \cos 47^{\circ}=$

• A

  $\frac{1}{32}(1+\sqrt{2}-\sqrt{3})$
• B

  $\frac{1}{16}(1+\sqrt{3}+\sqrt{5})$
• C

  $\frac{1}{16}(2+\sqrt{3}-\sqrt{5})$
• Correct answer
  D

  $\frac{1}{32}(1+2 \sqrt{3}-\sqrt{5})$

Hence, the correct answer is option: 'D'.