If the coefficient of ${x^7}$ in ${\left( {a{x^2} + \frac{1}{{bx}}} \right)^{11}}$ is equal to the coefficient of ${x^{ - 7}}$ in ${\left( {ax - \frac{1}{{b{x^2}}}} \right)^{11}}$, then $ab =$

  • [AIEEE 2005]
  • A

    $1$

  • B

    $1\over2$

  • C

    $2$

  • D

    $3$

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