D because you need to make the denominators have a common multiple.
A quadrilateral with only 2 right angles could be a trapezoid so Balavan is wrong. Denna is right because if 3 angles are right angles the the fourth angle must also be a right angle and has to be a square or rectangle.
I don't know, but I think we/you have to divide 5 into 6. If it is wrong, then i'm so sorry.