If $a_r$ is the coefficient of $x^r$ in the expansion of $(1 + x + x^2)^n$,then $a_1 - 2a_2 + 3a_3 - \dots - 2n\,a_{2n} = $

  • A
    $0$
  • B
    $n$
  • C
    $-n$
  • D
    $2n$

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