In a triangle $A B C$,
$\sin A \sin B+\cos A \cos B \sin C=1$
and the length of one of its sides is 1 . Let $s$ be the sum of the other two sides of $A B C$. Then

• A

  $s$ is always irrational and $s^2$ is always rational
• B

  $s$ and $s^2$ are always irrational
• Correct answer
  C

  either $s^2$ is rational or $(s-1)^2$ is rational
• D

  $s$ is rational

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