A square has two circles, one big and one small, which are tangent to each other and are all tangent to the square. The radius is R and r respectively. What is the length of the diagonal of the square?
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A$$( \sqrt { 2 } + 1 ) (r+R)$$
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B$$( \sqrt { 2 } - 1 ) (r+R)$$
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C$$\sqrt { 2 }( r+R)$$
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D$$( \sqrt { 2 } + 1 ) R + \sqrt { 2 } r$$
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E$$( \sqrt { 2 } + 1 ) r + \sqrt { 2 } R$$
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正确答案: A