$\int_{\pi / 6}^{\pi / 3} \cos ^{-4} x d x=$

• A

  $\frac{64}{9 \sqrt{3}}$
• B

  $\frac{52 \sqrt{3}}{9}$
• C

  $\frac{62 \sqrt{3}}{9}$
• Correct answer
  D

  $\frac{44}{9 \sqrt{3}}$

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