∫PE∨MB，PF∨MC，

∴ Quadrilateral PEMF is a parallelogram, (3 points)

∵ parallelogram ABCD,

∴AB=CD，

∵M is the midpoint of the edge AD,

∴AM=DM= 1:2 advertising,

∫AB:AD = 1:2，

∴ab=cd=am=dm(5 points)

∴∠ABM=∠AMB, ∠DMC=∠DCM, (6 points)

∫AD∨CB，

∴∠CBM=∠AMB, DMC=∠BCM, (7 points)

∴∠CBM=∠ABM= 1:2∠ABC，

∠DCM=∠BCM= 1:2∠DCB，

∫AD∨CB，

∴∠ ABC+∠ DCB = 180, (9 points)

∴∠MBC+∠MCB=90，

∴∠ BMC = 90, (10 point)

∴ parallelogram PEMF is rectangular. (12)

Hope to adopt, this is the second model problem of Fengxian District 20 10!