2.菱形的周长为20cm,两个相邻的内角的度数之比为1:2,则较长的对角线的长度是( )
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| A. | 20$\sqrt{3}$ | B. | 5$\sqrt{3}$cm | C. | $\frac{5}{2}$$\sqrt{3}$cm | D. | 5cm |