If two of the four expressions x + y, x + 5y, x - y, and 5x - y are chosen at random, what is the probability that their product will be of the form of x^2 - (by)^2, where b is an integer?
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A \frac{1}{2}
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B \frac{1}{3}
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C \frac{1}{4}
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D\frac{1}{5}
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E \frac{1}{6}