For number 9 on the test, it says to prove that NBC is isosceles. For the second statement, I said angle a = angle d, because of Theorem 35: The base angles in an isosceles trapezoid are equal. But when we checked it, it said angle a = angle d because of Theorem 36: The diagonals of an isosceles trapezoid are equal. But that does not make sense because I was trying to say that the angles are equal, not the diagonals. 

Thank you! ​