12.
如图,在?ABCD中,AE⊥BC于E,AE=EB=EC=a,且a是一元二次方程x2+2x-3=0的根,则?ABCD的周长为( )
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| A. | 4+2$\sqrt{2}$ | B. | 12+6$\sqrt{2}$ | C. | 2+2$\sqrt{2}$ | D. | 2+$\sqrt{2}$或12+6$\sqrt{2}$ |