If $\alpha, \beta \in \mathbb{R}$ are such that $1-2i$ (where $i^{2}=-1$) is a root of $z^{2}+\alpha z+\beta=0$,then $(\alpha-\beta)$ is equal to ..... .

  • A
    $-3$
  • B
    $-7$
  • C
    $7$
  • D
    $3$

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