The vertex of an equilateral triangle is $(2,-1)$ and the equation of its base in $x + 2y = 1$. The length of its sides is

  • A

    $4/\sqrt {15} $

  • B

    $2/\sqrt {15} $

  • C

    $4/3\sqrt 3 $

  • D

    $1/\sqrt 5 $

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