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 $$\frac{1}{6}$$