Suppose the coefficient of $x^7$ in $\left(a x^2+\frac{1}{b x}\right)^{11}$ is equal to the coefficient of $x^{-1}$ in $\left(a x-\frac{1}{b x^2}\right)^{11}$. Then

• A

  ${a b^2=\frac{2}{3}}$
• B

  $a^2=b$
• C

  $a=b^2$
• Correct answer
  D

  $a b=\frac{7}{5}$

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