If $|a| < 1$ and $b = \sum_{k=1}^{\infty} \frac{a^k}{k}$,then $a$ is equal to

  • A
    $\sum_{k=1}^{\infty} \frac{(-1)^k b^k}{k}$
  • B
    $\sum_{k=1}^{\infty} \frac{(-1)^{k-1} b^k}{k!}$
  • C
    $\sum_{k=1}^{\infty} \frac{(-1)^k b^k}{(k-1)!}$
  • D
    $\sum_{k=1}^{\infty} \frac{(-1)^{k-1} b^k}{(k+1)!}$

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