In each of the following statements, choose one word, parallelogram, rectangle, rhombus, trapezoid, kite, or square, so that the resulting sentence is true. If none of the words makes the sentence true, answer "none." a. A quadrilateral is a _____if, and only if, its diagonals are congruent and bisect each other. b. A quadrilateral is ______if, and only if, its diagonals are perpendicular and bisect each other. c. A quadrilateral is a _______ if, and only if, its diagonals are perpendicular bisectors of each other. d. A quadrilateral is a______ if, and only if, a pair of opposite sides are parallel and congruent.