If $\cos x + \cos y + \cos \alpha = 0$ and $\sin x + \sin y + \sin \alpha = 0,$ then $\cot \,\left( {\frac{{x + y}}{2}} \right) = $

  • A

    $\sin \alpha $

  • B

    $\cos \alpha $

  • C

    $\cot \alpha $

  • D

    $\sin \,\left( {\frac{{x + y}}{2}} \right)$

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