If $1 \cdot 3 \cdot 5 + 3 \cdot 5 \cdot 7 + 5 \cdot 7 \cdot 9 + \dots$ to $n$ terms $= n(n+1) f(n)$,then $f(2) =$

  • A
    $12$
  • B
    $42$
  • C
    $18$
  • D
    $20$

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