Which term of the sequence $( - 8 + 18i),\,( - 6 + 15i),$ $( - 4 + 12i)$ $,......$ is purely imaginary

  • A

    $5^{th}$

  • B

    $7^{th}$

  • C

    $8^{th}$

  • D

    $6^{th}$

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