Please Help!!!!

A student wrote the following sentences to prove that parallelogram ABCD has two pairs of opposite sides equal:

For triangles ABD and CDB, alternate interior angle ABD is congruent to angle CDB because AB and DC are parallel lines. Similarly, alternate interior angle ADB is equal to angle CBD because AD and BC are parallel lines. DB is equal to DB by reflexive property. Therefore, triangles ABD and CDB are congruent by SAS postulate. Therefore, AB is congruent to DC and AD is congruent to BC by CPCTC.

Which statement best describes a flaw in the student's proof?

Question

Please Help!!!!

A student wrote the following sentences to prove that parallelogram ABCD has two pairs of opposite sides equal:

For triangles ABD and CDB, alternate interior angle ABD is congruent to angle CDB because AB and DC are parallel lines. Similarly, alternate interior angle ADB is equal to angle CBD because AD and BC are parallel lines. DB is equal to DB by reflexive property. Therefore, triangles ABD and CDB are congruent by SAS postulate. Therefore, AB is congruent to DC and AD is congruent to BC by CPCTC. 

Which statement best describes a flaw in the student's proof?

anonymous · Answer

Angle ADB is congruent to angle CBD because they are vertical angles.
 Angle ADB is congruent to angle CBD because they are corresponding angles.
 Triangles ABD and CDB are congruent by SSS postulate.
 Triangles ABD and CDB are congruent by SAS postulate.

anonymous · Answer

what do you think?

anonymous · Answer

attachment

anonymous · Answer

I am almost sure it is D, however, not too confident on this one.

anonymous · Answer

i think your right! >:}

anonymous · Answer

Okay! :) Thank you, Joker. :D Wish me luck!!

anonymous · Answer

wait.. wheres my medal >:p

anonymous · Answer

thanks >:} and i hope you do well

anonymous · Answer

Lol, sorry about that, I was just putting in my answer! Medal has been justly awarded. :D

anonymous · Answer

Sorry here take mine ;)