Which completes the syllogism? all quadrilaterals have four sides. all squares are quadrilaterals. therefore,

all polygons are squares.
all squares have four sides.
all squares are parallelograms.
all squares are polygons.

Given: ae ≅ ce ; de ≅ be prove: abcd is a parallelogram. we have that ab || dc. by a similar argument used to prove that △aeb ≅ △ced, we can show that △ ≅ △ceb by. so, ∠cad ≅ ∠ by cpctc. therefore, ad || bc by the converse of the theorem. since both pair of opposite sides are parallel, quadrilateral abcd is a parallelogram.