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The expression $$x^{4}+2x^{2}y^{2}+9y^{4}$$ is equivalent to which of the following?
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A.$$(x^{2}+3y^{2})^{2}$$
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B.$$(x^{2}+3y^{2})(x^{2}+3y^{2})$$
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C.$$(x^{2}+3y^{2}+xy)^{2}$$
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D.($$x^{2}+2xy+3y^{2}$$)($$x^{2}-2xy+3y^{2}$$)
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E.($$x^{2}+2xy-3y^{2}$$)($$x^{2}-2xy-3y^{2}$$)
D显示答案
