If x and y are positive real numbers, the operation △ is defined by x△y=xy/(x+y). Let a, b, and c be positive real numbers. Which of the following is equivalent to 1/a△(1/b△1/c)?
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A(a+b+c)/abc
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B(ab+bc+ac)/abc
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C1/(a+b+c)
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D(ab+bc+ac)/(a+b+c)
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Eabc/(a+b+c)
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正确答案: C