Question

Melissa writes the following proof for the theorem: If the diagonals of a quadrilateral bisect each other, the quadrilateral is a parallelogram:

Melissa's proof

1. For triangles AOB and COD, angle 1 is equal to angle 2 as they are vertical angles.
2. AO = OC and BO = OD because it is given that diagonals bisect each other.
3. The _______________ are congruent by SAS postulate.
4. Similarly, triangles AOD and COB are congruent.
5. By CPCTC, AB is equal to DC.
6. By CPCTC, AD is equal to BC.
7. As the opposite sides are congruent the quadrilateral ABCD is a parallelogram

Answer 1

Which is the missing phrase in Melissa's proof?

angles ADB and CBD
angles AOB and COD
triangles ADB and CBD
triangles AOB and COD

Answer 2

some help!!