Let $S=\{1,2,3, \ldots \ldots, n\}$ and $A=\{(a, b) \mid 1 \leq$ $a, b \leq n\}=S \times S$. A subset $B$ of $A$ is said to be a good subset if $(x, x) \in B$ for every $x \in S$. Then, the number of good subsets of $A$ is

  • [KVPY 2012]
  • A

    $1$

  • B

    $2^n$

  • C

    $2^{n(n-1)}$

  • D

    $2^{n^2}$

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