Find the sum to the indicated number of terms in the geometric progression: $1, -a, a^{2}, -a^{3}, \ldots$ to $n$ terms (if $a \neq -1$).

  • A
    $\frac{1-(-a)^{n}}{1+a}$
  • B
    $\frac{1+(-a)^{n}}{1+a}$
  • C
    $\frac{1-(-a)^{n}}{1-a}$
  • D
    $\frac{1+(-a)^{n}}{1-a}$

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