Reason: Quadrilateral ABCD and Quadrilateral AEFD are parallelograms.

∴AD//=BC

AD//=EF

∴BC//=EF

∴ Quadrilateral BCEF is a parallelogram.

1: parallelogram

∫BD is the center line of triangle ABC.

∴ bisecting vertex angle

Similarly, the other group is equally divided.

∴ Quadrilateral AECF is a parallelogram