In a rectangular coordinate system, point A has coordinates (d, d), where d > 0. Point A and the origin form the endpoints of a diameter of circle C. What fraction of the area of circle C lies within the first quadrant?
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A$${\pi}\over{\pi+\sqrt{2}}$$
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B$${\pi}\over{\pi+1}$$
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C$$\sqrt{\frac{2}{\pi}}$$
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D$${\pi+2}\over{2{\pi}}$$
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E$${2\pi}\over{2{\pi}+1}$$
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正确答案: D