Question $3(10$ points$)$

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Assume $A$ is the set of positive integers less than $3$ and $B$ is the set of positive integers less than $4$ and $R$ is a relation from $A$ to $B$ and $R=\{(1,2),(1,3),(2,1),(2,3)\}$ Which of the following describes this relation?

$\{(a,b)|ainA,$BinB,$ab\}$

$\{(a,b)|ainA,$BinB,$a=b\}$

$\{(a,b)|ainA,$BinB,$a>b^{{?}^{?}}b>a\}$

$\{(a,b)|ainA,$BinB,$b=a+1\}$