$\sum_{\substack{i, j=0 \\ i \neq j}}^{n} {}^{n}C_{i} {}^{n}C_{j}$ is equal to

  • A
    $2^{2n} - {}^{2n}C_{n}$
  • B
    $2^{2n-1} - {}^{2n-1}C_{n-1}$
  • C
    $2^{2n} - \frac{1}{2} {}^{2n}C_{n}$
  • D
    $2^{n-1} + {}^{2n-1}C_{n}$

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