Two radioactive materials $A$ and $B$ have decay constants $10\lambda$ and $\lambda$,respectively. If initially they have the same number of nuclei,then the ratio of the number of nuclei of $A$ to that of $B$ will be $1/e$ after a time:

  • A
    $\frac{1}{11\lambda}$
  • B
    $\frac{1}{10\lambda}$
  • C
    $\frac{1}{9\lambda}$
  • D
    $\frac{11}{10\lambda}$

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