If the coefficient of $3^{\text {rd }}$ term from the beginning in the expansion of $\left(a x^2-\frac{8}{b x}\right)^9$ is equal to the coefficient of $3^{\text {rd }}$ term from the end in the expansion of $\left(a x-\frac{2}{b x^2}\right)^9$ then the relation between $a$ and $b$ is

• A

  $a b=-1$
• B

  $a b=1$
• Correct answer
  C

  $a^5 b^5=-2$
• D

  $a^5 b^5=2$

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