∫FG is the center line of the right-angled trapezoidal AECD ∠ B = ∠ B' = 90,

∴FG∥BC∥AD，

∴∠bef=∠feb′=∠efb′，

∴eb′=ef=af=fb′，

∴∠aeb′=60，

∫AB = AB′= 23，

∴AE=4.

So choose D.