∵ Quadrilateral ABCD is a parallelogram

∴AB=CD,AB∥CD

∴∠BAO=∠DCO (two straight lines are parallel and the internal dislocation angles are equal)

∠AOB=∠COD (equal to vertex angle)

∴ Triangle ABO≌ Triangle COD

∴AO=CO,BO=DO.

(2).

Because ABCD

It is a parallelogram.

therefore

OB=OD

OE=OF

therefore

BFDE is a parallelogram (a quadrilateral with its diagonal bisected is a parallelogram.

)