If $n$ be odd or even, then the sum of $n$ terms of the series $1 - 2 + $ $3 - $$4 + 5 - 6 + ......$ will be

  • A

    $ - \frac{n}{2}$

  • B

    $\frac{{n - 1}}{2}$

  • C

    $\frac{{n + 1}}{2}$

  • D

    (a) and (c) both

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