If k is a two-digit positive integer with tens digit x and units digit y, then $${k}^{2}$$ =
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A$${10}{x}^{2}+{y}^{2}$$
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B$${100}{x}^{2}+{y}^{2}$$
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C$${100}{x}^{2}+{10}{x}{y}+{y}^{2}$$
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D$${100}{x}^{2}+{20}{x}{y}+{y}^{2}$$
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E$${100}{y}^{2}+{20}{x}{y}+{x}^{2}$$
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正确答案: D