∵ Fold along a straight line passing through point A, so that AC falls on the edge of AB.

∴∠BAD=∠CAD

Grinding EF folding

∴EF vertical division advertisement

∴EA=ED,FA=FD

Let the intersection of AD and EF be o.

∠AOE=∠AOF=90, ∠EAO =∠ FAO, AO=AO.

∴△EAO≌△FAO

∴AE=AF

∴AE=AF=DE=DF

A quadrilateral is a diamond.