Premise: "A boy stands on a rail with his arms outstretched."\nHypothesis: "A sad boy stands on a rail with his arms outstretched."\nDo we know that the hypothesis entailed by the premise?
Think hard. Detailed solution:
it is not possible to tell
Standing on a rail with outstretched arms does not indicate mood/emotion such a being sad.

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Final answer: it is not possible to tell