If $\mathrm{A}(0,3,4), \mathrm{B}(1,5,6), \mathrm{C}(-2,0,-2)$ are the vertices of a triangle ABC and the bisector of angle A meets the side BC at D, then $\mathrm{AD}=$

• A

  $\frac{\sqrt{21}}{5}$
• Correct answer
  B

  $\frac{\sqrt{42}}{10}$
• C

  $10$
• D

  $4$

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