The interval in which the function
$f(x)=\log _{\frac{1}{2}}\left(x^2-2 x-8\right)$
is monotonically increasing, is

• A

  $(4,+\infty)$
• Correct answer
  B

  $(-\infty,-2)$
• C

  $(-\infty, 4)$
• D

  $(-2,+\infty)$.

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