如图所示,梯形A 1 B 1 C 1 D 1 是一平面图形ABCD的直观图(斜二测),若A 1 D 1 ∥O 1 y 1 ,A 1 B 1 ∥C 1 D 1 ,A 1 B 1 =C 1 D 1 =2,A 1 D 1 =1,则ABCD的面积是 [ ] A.10 B.5C.5 D.10