HELP: Which of the following is NOT a sufficient method to prove that a quadrilateral is a parallelogram

I Need help, im not so good in geometry:(( i really need this credit to move on and i dont want to fail, please help!
Question:
Which of the following is NOT a sufficient method to prove that a quadrilateral is a parallelogram?
A. Show both paris of opposite sides are congruent
B. Show that one pair of opposite sides are both parallel and congruent
C. Show that the diagonals are perpendicular
D. Show that the diagonals bisect each other

C

If the diagonals are perpendicular, it could be a trapezoid.









You are very attractive!

C

Here's a geometric figure known as a kite:
http://en.wikipedia.org/wiki/File:Geomet…
It has perpendicular diagonals, but it is not a parallelogram