In triangle ABC, if $\mathrm{a}=13, \mathrm{~b}=8, \mathrm{c}=7$, then $\cos (\mathrm{B}+\mathrm{C})=$

• A

  $\frac{11}{13}$
• B

  $\frac{23}{26}$
• C

  $\frac{3}{4}$
• Correct answer
  D

  $\frac{1}{2}$

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