∫△ABC and△△△ def are equilateral triangles, and O is the midpoint of BC and EF.

∴AO⊥BC,DO⊥EF,∠EDO=30, ∠ package =30,

∴ od: OE = OA: ob = root number 3: 1,

∠∠ Doe +∠EOA =∠ Boya +∠EOA means ∠ Doe =∠EOB,

∴△DOA∽△EOB，

∴ OD: OE = OA: OB = AD: BE = root number 3: 1.

So choose a.