The possible 6 pairs of requirements are: H.S & Exp, H.S & Vet, H.S & Ref, Exp & Vet, Exp & Ref and Vet & Ref.
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After filling the table with the given statements, it looks like:
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H.S Exp Vet Ref
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A ã
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B ã ã
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C ã ã
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D ã ã
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After canceling the 3 pairs given, the pairs that are left are H.S & Exp, H.S & Ref and Vet & Ref.
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Now, filling the table for these pairs:<o:p></o:p>
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Vet & Ref:<o:p></o:p>
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If placed this for A, then H.S. and Vet will be common to both A & B. this is a contradiction.
If placed this for B, there is no contradiction so there is a chance.
If placed this for C, then Exp and Ref will be common to both C & D. this is a contradiction.
If placed this for D, then Exp and Vet will be common to both C & D. this is a contradiction.
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So, the table after filling the pair Vet & Ref is:
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H.S Exp Vet Ref
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A ã
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B ã ã ã
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C ã ã
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D ã ã
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After filling the table one more pair H.S and Ref is also satisfied.
The only pair now left is H.S & Exp.
<o:p> </o:p>
If placed this for A, there is no contradiction so there is a chance.
If placed this for B, then Exp and Vet will be common to both B & C. this is a contradiction.
If placed this for C, then H.S and Vet will be common to both B & C. this is a contradiction.
If placed this for D, then H.S and Ref will be common to both B & D. this is a contradiction.
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So, the table after filling the pair Vet & Ref is:
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H.S Exp Vet Ref
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A ã ã
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B ã ã ã
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C ã ã
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D ã ã
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From the final table it is obvious the person going to be selected is B (Brent).