If $x$ is parallel to $y$ and $z$ where $x = 2i + j + \alpha k$,$y = \alpha i + k$ and $z = 5i - j$,then $\alpha$ is equal to

  • A
    $ \pm \sqrt{5} $
  • B
    $ \pm \sqrt{6} $
  • C
    $ \pm \sqrt{7} $
  • D
    None of these

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