Answer: I believe the answer is C
Explanation:
This is what I want you to do. Draw a kite like the one I did (include the dotted lines going). The add in that 90 degree sign to the corner of the dotted line. This is your working
In your reasoning you can say that If a quadrilateral is a kit, the diagonals will always be perpendicular. Then use that image as your proof.
Soz for the late reply :)