If $\mathrm{A}(2,-1,1), \mathrm{B}(2,5,1)$ and $\mathrm{C}(0,-2,3)$ are the vertices of a triangle. If D is the point of intersection of the side BC and the internal angular bisector of angle A, then $\mathrm{AD}=$

• A

  $\frac{5}{\sqrt{7}}$
• B

  $\frac{3}{\sqrt{2}}$
• C

  $\frac{\sqrt{3}}{2}$
• Correct answer
  D

  $\frac{4}{\sqrt{3}}$

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