$\int \frac{\sec ^2 x}{\sin ^7 x} d x-\int \frac{7}{\sin ^7 x} d x=$

• Correct answer
  A

  $\frac{1}{\sin ^6 x \cos x}+c$
• B

  $\frac{\tan x}{\sin ^8 x}+c$
• C

  $\sin ^8 x \cos x+c$
• D

  $\sec x \tan ^7 x+c$

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