The table below shows the steps to prove that if the quadrilateral ABCD is a parallelogram, then its opposite sides are congruent:

Statement Reasons
1 AB is parallel to DC and AD is parallel to BC Definition of parallelogram
2 angle 1 = angle 2, angle 3 = angle 4 If two parallel lines are cut by a transversal then the alternate interior angles are congruent
3 BD = BD
4 triangles ADB and CBD are congruent If two angles and the included side of a triangle are congruent to the corresponding angles and side of another triangle, then the triangles are congruent
5 AB = DC,
AD = BC Cor.

Question

The table below shows the steps to prove that if the quadrilateral ABCD is a parallelogram, then its opposite sides are congruent: 

Statement	Reasons
1	AB is parallel to DC and AD is parallel to BC	Definition of parallelogram
2	angle 1 = angle 2, angle 3 = angle 4	If two parallel lines are cut by a transversal then the alternate interior angles are congruent
3	BD = BD	
4	triangles ADB and CBD are congruent	If two angles and the included side of a triangle are congruent to the corresponding angles and side of another triangle, then the triangles are congruent
5	AB = DC, 
AD = BC	Cor.