If $C_j = {}^{n}C_j$,then $C_0 C_r + C_1 C_{r+1} + C_2 C_{r+2} + \ldots + C_{n-r} C_n = $

  • A
    $\frac{(2n)!}{(n-r)!(n+r)!}$
  • B
    $\frac{(2n)!}{(n-2r)!(n+2r)!}$
  • C
    $^{2n}C_{n+r}$
  • D
    $^{2n}C_{r}$

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