In a $\triangle A B C$ if $a+c=5 b$, then $\cot \frac{A}{2} \cot \frac{C}{2}=$

• A

  2
• B

  $\frac{1}{2}$
• Correct answer
  C

  $\frac{3}{2}$
• D

  $\frac{2}{3}$

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