Which of these relations is transitive?

1. A.

   R = {(1, 2), (2, 3), (1, 3)}

2. B.

   R = {(1, 2), (2, 3), (3, 1)}

3. C.

   R = {(1, 2), (2, 1), (3, 2)}

4. D.

   R = {(1, 2), (2, 1), (3, 3)}

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