In the binomial expansion of $(a-b)^n, n \geq 5$, the sum of the $5^{\text {th }}$ and $6^{\text {th }}$ terms is zero. Then the value of $\frac{a}{b}$ is

• A

  $\frac{n-2}{3}$
• Correct answer
  B

  $\frac{n-4}{5}$
• C

  $\frac{n-5}{7}$
• D

  $\frac{n-1}{3}$

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